Exploring a Co-Teaching Model to Teach Energy and Food Systems in STEM Integration Through the Lens of Pedagogical Content Knowledge

Abstract

The researchers of this qualitative case study explored an interdisciplinary collaboration in STEM integration through the lens of pedagogical content knowledge (PCK). We examined a co-teaching integrated STEM model of a biology teacher and a family consumer sciences (FCS) teacher who collectively taught 38 students in an urban secondary high school in the United States. We aimed to answer, “in what ways did the biology teacher and FCS teacher demonstrated their PCK in integrated STEM to teach energy through food systems?” The results showed energy was not the centerpiece in the integrated STEM lessons that teachers developed even though the overarching problem focused on food waste as wasted energy. The two teachers’ different disciplinary thinking and professional identities informed their pedagogical knowledge. In addition, when teachers developed integrated STEM lessons, their knowledge of students’ preconceptions was not positioned to emphasize students’ learning difficulties related to certain concepts, but helped them identify what students needed most in their daily learning. The teachers taught within their disciplinary knowledge and experiences when they designed integrated STEM instruction. Teachers may change their PCK by working collaboratively with teachers from other disciplines, but this may take multiple successions and years for teachers to understand and develop their collaborative PCK.

1. Introduction

Tackling real-world problems is a common feature when using integrated science, technology, engineering, and mathematics (STEM) pedagogical design (Wang & Knobloch, 2022; Guzey et al., 2020; Moore et al., 2020; National Academy of Engineering [NAE] & National Research Council [NRC], 2009; National Research Council [NRC], 2014). Integrated STEM teaching emphasizes decompartmentalizing disciplinary boundaries to help students make interdisciplinary connections through solving complex real-world problems (Moore et al., 2020; National Research Council [NRC], 2012; National Research Council [NRC], 2014; National Science & Technology Council [NSTC], 2018). Due to the interdisciplinary nature of real-world problems, teachers need additional professional knowledge to develop educational materials and implement integrated STEM instruction. Teachers are active agents of education, who act based on their own knowledge and ideas (Dewey, 1908; Schwab, 1954/1978). Teachers’ conceptions and knowledge about STEM integration inform how they plan and implement STEM integration (Wang et al., 2020; Dare et al., 2019).

Teachers’ professional knowledge has been a longstanding topic of interest to researchers in the field of education. Pedagogical content knowledge (PCK) is a special type of knowledge that teachers need to deliver effective instruction (Shulman, 1986, 1987). PCK is topic, person, and context-specific (Şen et al., 2018), and it focuses on specific content, concepts, and vocabularies regarding the topic of interest (Birdsall, 2014). Although PCK has been extensively studied in science education and mathematics education (Chan & Hume, 2019), few integrated STEM researchers have studied PCK. When applying integrated STEM instruction, teachers tend to lean towards a specific level of integration, select the most suitable implementation design, and place emphasis on different parts of STEM based on their subjects and needs (Wang et al., 2020; Herschbach, 2011). Teachers’ individual needs and professional identity likely play critical roles when teachers plan and implement integrated STEM lessons and instruction.

There are different models of STEM integration, such as individual teaching, co-teaching, and team-teaching (Moore et al., 2020). Different models exist because of various reasons. For example, elementary teachers tend to use an individual teaching model because one teacher tends to teach all STEM subjects in their classroom. Middle and high school teachers are inclined to use either co-teaching or team-teaching models because STEM subjects are typically taught separately and tend to have disciplinary-specific curricula (Herschbach, 2011). Teachers do not have sufficient knowledge to teach other STEM subjects or they do not share the same students in their classrooms (Wang et al., 2020; Guzey et al., 2020). We were interested in exploring collaborative PCK of integrated STEM because PCK as a topic, person, and context-specific (Şen et al., 2018) can inform how teachers design their integrated STEM instruction based on their needs, how teachers use co-teaching or team-teaching STEM integration, and how they conceptualize their abilities and feasibilities to collaborate with their peers.

The researchers explored how a science teacher (biology) and a Career Technical Education (CTE) teacher (Family and Consumer Sciences, FCS) developed integrated STEM instruction as an interdisciplinary team. The teachers used the co-teaching integrated STEM model to develop their integrated STEM lessons. The integrated STEM lessons and instruction focused on teaching energy through food systems. When collaborating with each other, we investigated “in what ways did the biology teacher and FCS teacher demonstrate their PCK in integrated STEM to teach energy through food systems?” We used four subset questions to unpack the PCK in a co-teaching integrated STEM model.

• What was the overarching issue that the biology teacher and the FCS teacher used to structure their lessons regarding energy and food systems?
• What energy content knowledge did the teachers conceptualize, and how did they teach energy concepts through food systems?
• What topic-specific pedagogical knowledge did the teachers use in teaching energy by using food systems?
• What were students’ preconceptions and learning difficulties that teachers knew? How did their instructional design (lesson planning and implementation) address students’ preconceptions and learning difficulties?

In this article, we frame the study with literature grounded in pedagogical content knowledge and integrated STEM instructional design. Next, we explain the materials and methods we used to conduct the study. Then, we present the results, discussion, limitations, and conclusion.

2. Background Literature and Theoretical Perspective

2.1. Pedagogical Content Knowledge

PCK is a unique knowledge domain that interwoven pedagogy and subject matter knowledge necessary for supporting effective teaching and learning (Shulman, 1987). PCK has been extensively studied by numerous scholars over the years. There are different PCK models that are structured by combining two (such as Shulman’s (1986) model) to five components (such as S. Park and Chen’s (2012) pentagon model; Magnusson et al.’s (1999) model). Researchers suggested PCK is both knowledge and practices of teachers (Gess-Newsome, 2015; Gess-Newsome et al., 2019). As knowledge, PCK has different constructs and components (e.g., topic-specific knowledge, knowledge of instructional strategy, knowledge of curriculum, and knowledge of assessment). In addition, PCK also considers teachers’ classroom practices, such as declarative and dynamic PCK (Alonzo & Kim, 2015). Although how teachers develop their PCK is still not clear to researchers, some researchers suggest the development of PCK could be specific to individuals depending on personal experience or through group collaboration (Gess-Newsome, 2015; Carlson et al., 2019). One of the current trends of PCK research is to examine interactions among PCK components, especially the relationship between content knowledge and PCK (Şen et al., 2018).

There has been limited PCK research in STEM integration. Preservice elementary teachers’ integrated nature of PCK was integrating basic measurement into science activities as a common integrative strategy (An, 2017). For example, preservice elementary teachers explored ratios connecting physics and algebra, and they conducted experiments with heredity to demonstrate connections between biology and probability. In a study of PCK for integrated STEM development, preservice chemistry teachers were able to integrate at least two STEM disciplines in their lessons, and few pre-service teachers were able to balance STEM disciplines in their integrated STEM lessons (Aydin-Gunbatar et al., 2020). Next, high school biology and mathematics teachers’ PCK for integrated STEM and found that biology and math teachers defined integration differently (Weinberg & McMeeking, 2017). Biology teachers conceptualized integrated STEM teaching as being more aligned with content integration (Moore et al., 2014), and mathematics were used to discover and describe scientific phenomena. In comparison, mathematics teachers conceptualized integrated STEM teaching aligned more with context integration (Moore et al., 2014), and science was used to provide concrete examples to help students learn and apply specific math content. Although researchers attempted to describe the integrated nature of PCK of teachers who taught integrated STEM instruction, these studies did not address critical PCK components, such as teachers’ knowledge of appropriate topic-specific instructional strategies and representation, and their understanding of students’ learning difficulties and preconceptions.

We adapted Mthethwa-Kunene et al.’s (2015) PCK model, which is supported by Gess-Newsome (2001, 2015) as the theoretical framework. The model combines three components: content knowledge, pedagogical knowledge, and knowledge of students’ preconceptions and learning difficulties. We used energy and its role in food systems, a topic-specific construct (Veal & MaKinster, 1999) of PCK, as the content knowledge of PCK in this study. For pedagogical knowledge, we particularly explored what pedagogy (e.g., didactic teaching, inquiry-based instruction) that teachers used to structure integrated STEM lessons. Further, we focused on the teachers’ understanding of their students’ preconceptions and learning difficulties regarding energy and food systems.

2.2. Integrated STEM Instructional Design

STEM integration involves embedding STEM education and activities into classrooms, with a goal of teaching students how to solve complex real-world problems, think critically, and prepare for future STEM careers (National Research Council [NRC], 2012). In the context of food systems, examples of complex real-world problems can be food insecurity, food waste, renewable energy, environmental sustainability, and climate change. In the past two decades, STEM integration has attracted considerable attention in educational research, yet it is interpreted in various ways. Developing a precise definition of integrated STEM education has been a challenge. Currently, there is no unifying STEM integration framework or a consensus definition of STEM integration (Moore et al., 2020). Moore et al. (2020) conducted a literature review to explore how current research defines, conceptualizes, and operationalizes STEM integration. They synthesized 109 articles and summarized key features of STEM integration. They found using complex real-world problems was a common substantial feature of integrated STEM instruction. Moore et al. (2020) concluded that STEM integration looks different based on the number of STEM subjects, number of teachers, and the role of individual discipline and pedagogies applied. How these factors come together results in different models of STEM integration. Teachers make instructional decisions based on their individual needs and adapt integrated STEM models that are most suitable for them to use in their classrooms (Wang et al., 2020). Because of the academic and CTE content co-teaching model used in this study, we defined STEM integration as:

intentionally and purposively blending multiple disciplines (i.e., academic and vocational) to help students meaningfully learn and apply academic content through real-world problems framed in designed complex systems and grounded in career and technical contexts that facilitate multidisciplinary, interdisciplinary, or transdisciplinary learning for the development of life-long and workforce development connections and skills.

(Wang & Knobloch, 2023, p. 252)

3. Materials and Methods

This qualitative research study used a case study design. We chose a case study design because we wanted to conduct an in-depth exploration of the richness and complexity of two teachers’ perspectives of PCK in a bounded system, which was a specific unit of integrated STEM instruction co-designed and co-taught by two teachers in the same classroom with the same students). The case study design affords researchers to use multiple methods of data collection and data sources to generate knowledge to inform professional practice (Bloomberg, 2018). The researchers aimed to explore the two teachers’ content knowledge, pedagogical knowledge, and knowledge of students’ preconceptions and learning difficulties (Mthethwa-Kunene et al., 2015) in a bounded experience, which is using integrated STEM instructions to teach an energy concept through food systems. The epistemology that the researchers held aligned with constructivism, which suggests that qualitative researchers sought to understand the meaning and knowledge that are based on constructed social reality through our investigation and the results are interpreted by the researchers (Merriam, 1998). Therefore, the case study design was aligned with Stake’s (1995) and Merriam’s (1998) epistemology. We defined case as “a phenomenon of some sort occurring in a bounded context” (Merriam, 1998, p. 27), and we gave meaning to the data through consolidating, reducing, and interpreting what the teachers have said and what the researcher has seen and read (Merriam, 1998).

3.1. The Teachers and the School’s Profile

Two Caucasian female teachers participated in the study. Jane, the biology teacher, and Marcy, the family and consumer sciences teacher, each had over 25 years’ teaching experience as high school teachers. Prior to this study, Jane and Marcy had never co-taught a class before. Jane and Marcy used a co-teaching model, where they utilized the advanced food technology class to implement their integrated STEM instruction. They taught in a traditional public high school in a U.S. city with a population of 100,000. A traditional public high school is operated by a school district, governed by a local board, funded by state and local taxes, and follows the requirements of the state department (Smith, 2014). Nearly two-thirds of the students were economically disadvantaged. The student population was 32% Caucasian, 32%, African American, 25% Hispanic, and 10% multiracial during the 2021 school year when data were collected. Students’ mathematics and science proficiencies were below the state average.

3.2. Integrated STEM Teacher Professional Development

Teachers were recruited based on their professional teaching experience in public education, interests in STEM integration and the food system, and motivation to collaboratively design and implement an integrated STEM project for their students. The teachers participated in a year-long teacher professional development (TPD) program that was designed by the authors and STEM experts. The TPD aimed to increase high school teachers’ integrated STEM teaching capacity through food systems. During the TPD, the teachers completed 10 asynchronous online learning modules and attended two days of synchronous learning experience by interacting with teacher educators, scientists, and engineers. The key content of the TPD included introduction of STEM integration, developing integrated STEM lessons and instruction, level of STEM integration, agroecosystem thinking, and assessing integrated STEM outcomes. Agroecosystem thinking is holistically analyzing problems and considering the role environmental sustainability, production efficiency, economic viability, and social responsibility play a role in food systems (Agunga et al., 2005). After the TPD, teachers formed a collaborative team to co-develop and implement integrated STEM lessons and instruction that focused on teaching energy through food systems. The TPD provided examples of integrated STEM lessons and provided teachers freedom to choose whether to use the lessons that were provided or develop STEM lessons that were most suitable for their classes and school environments. In this study, the two teachers chose to develop their own integrated STEM lessons, and the lessons were lined by the big idea of “prevent apple waste by applying different ways to extend apple shelf life”.

3.3. Data Collection

The researchers used a variety of data sources (

Table 1. Data collection and data sources.

Data Collection	Data Sources
Pre-lesson Reflection (R)	Teachers’ written responses to six questions
Team (T) and semi-structured Interviews (I)	Transcripts of a team interview and each teacher’s individual interview
Lesson Observations (O)	Ten video recordings
Concept Mapping Exercise (C)	Teachers’ individual concept maps
Lesson Plans (L)	Eight lessons (four lessons per teacher)

Note: The abbreviations are also used in the results to indicate the data sources.

) that included a pre-lesson reflection, semi-structured interviews (a 70 min team interview and a 60 min individual interview), lesson observation through video recordings, concept mapping, and final lesson plans. Data sources were triangulated during the coding process to enhance the validity of findings.

3.4. Pre-Lesson Reflection

Instead of conducting a pre-interview, this study used a pre-lesson reflection that adapted from Loughran et al.’s (2012) study to collect baseline information from the teachers. The teachers were asked six questions before they planned their integrated STEM lessons. The six questions were:

(1)

Do you normally teach about energy transfer? Please describe how you teach energy transfer.

(2)

How will the lessons you teach incorporate energy transfer? Please answer these questions, what I will do, what will the students do, what will students know, what might students not know, and what is the rationale?

(3)

What are potential connections between energy transfer and the subtopics of the lesson plan?

(4)

Why would energy transfer important to your students’ overall curriculum and the food system problems?

(5)

What do you expect students will typically know about energy transfer (e.g., prior knowledge or misconceptions) when they come to class?

(6)

What do you expect students to struggle with when they learn energy transfer?

3.5. Semi-Structured Interviews: A Team Interview and a Post Interview

After teachers implemented their integrated STEM lessons, we conducted a team interview and an individual interview with Jane and Marcy. The team and individual interviews were conducted at different times on the same day. The team interview focused on Jane and Marcy’s experiences regarding how they co-developed and co-taught their integrated STEM lessons. The team interview was about 70 min long. During the team interview, we asked both Jane and Marcy when they worked together: (1) How did they decide the overarching food issue that they wanted to use to structure their integrated STEM lessons? (2) How did they decide the energy and food system content knowledge/concepts that would be taught? (3) How did they decide what topic specific instructional strategies would be used to teach energy and food systems? (4) What students’ preconceptions and learning difficulties did they need to be familiar with to teach energy and food systems; and (5) What did the teachers learn by working with each other to teach these integrated STEM lessons?

The individual interviews were about 60 min. Instead of thinking about working with their peers in an interdisciplinary team, we asked Jane and Marcy to answer the similar five questions that we used to structure the team interview, but on an individual level. For example, we changed question one to how the teachers decided the overarching food issue that they wanted to use to structure their integrated STEM lessons.

3.6. Lesson Observations Through Video Recordings

We used Swivl, an auto robot camera, to track and record the teachers while they taught their integrated STEM lessons. There were 10 video recordings that we collected for the study. Due to Jane and Marcy using the co-teaching model, both teachers appeared in most of the videos regardless of who was teaching. Determined by the content, the length of videos was between 12 min (e.g., students were reporting their final design solutions) to 46 min (e.g., Jane was teaching the introduction to selective breeding). The lesson observation focused on the teachers’ instructional approaches, such as what content was taught, what teaching approaches were used, as well as how the teachers interacted with students.

3.7. Concept Mapping

We adapted Mthethwa-Kunene et al.’s (2015) concept mapping exercise to explore how Jane and Marcy considered the key concepts (i.e., energy and food systems) connected with each other. Jane and Marcy individually drew a concept map to illustrate their ideas (Figure 1 and Figure 2). Teachers were asked three topics they could teach in their discipline for their grade level to guide the concept mapping activity: (1) key energy concept(s); (2) key food system concepts; and (3) draw a concept map that represents in a graphical fashion the relationship between the listed key concepts for the grade level of curriculum that they taught. Jane and Marcy were asked to indicate the relationships between energy and food systems by connecting lines with linking words or phrases in their concept maps.

Jane and Marcy created eight lesson plans (four per teacher), covering both the biological and culinary aspects of apples. The length of the lessons was about four weeks. The unit began with Jane’s four lessons and included an overview about apples, genetics of apples, energy (calories) and nutrition, and oxidation. The overview included place of origins of apples varieties, environments where apples thrive, and the life cycle of an apple tree. After students received a broad overview of apples, Jane introduced students to apple genetics and how we obtain new varieties through breeding and grafting. Next, Jane discussed the chemical make-up of apples, explored why apples are considered to be nutritious, and how our bodies use them for energy. Jane’s final lesson explored oxidation and ways to stop apples from browning or rotting.

After students biologically explored apples, Marcy taught the next four lessons on culinary uses of apples. The lessons included varieties and how to select the best apples for different purposes, techniques for preparation, creating a food product, and taste and sensory testing. In the first lesson, students explored what variety was the best for baking, eating as a snack, and dehydrating by looking at factors like an apple being firm or tender, or sweet versus tart. Following this lesson, students engaged in dehydrating the apples they selected as the best variety. Students learned safe and proper ways to peel, core, and slice apples to prepare them for dehydration. They also learned how to add antioxidants in the form of lemon juice and water to prevent browning. Building on students’ skills, the third lesson focused on creating a cooked product in the form of apple sauce, and how apple sauce can be used in other recipes like apple pumpkin bread. Marcy’s final lesson was a taste test and a comparison of the products students made. Students utilized food sensory skills to determine which had the best taste. Together, this collection of lessons engaged students in a scientific exploration of apples beginning with historical elements, technical aspects, and ending with applications and skill development.

3.8. Data Analysis and Reliability

ATLAS.ti 2.2, a qualitative data analysis software, was used to analyze the data. Four researchers analyzed the interview data according to the research interview analysis protocol. All data sources were analyzed across the three cycles. These data sources were used to triangulate and provide additional examples and evidence to the findings.

Guided by a constructivist epistemology, the researchers conducted consolidation, reduction, and interpretation through three cycles of data analyses (Merriam, 1998). In the first cycle of data analysis, the researchers used descriptive coding to code sentences from the transcripts with numbered lines. Descriptive coding summarizes sentences in a small structure like a single or two words to cover the basic topic of a piece of data collected (Saldaña, 2013). For example, a code of “teaching photosynthesis” that associated with the interview quotes included (but not limited to) “If I did photosynthesis, they [students] would have a worksheet”, “If you are doing in biology class…you can teach photosynthesis, say one week”, and “Photosynthesis, nobody can explain what goes on in the plant. It just too small and they [students] don’t work with plants”. The same code, teaching photosynthesis, that was used to code the concept map included (but was not limited to) “photosynthesis—process to grow”, “nutrients”, and “cellular respiration and material exchanges”.

Theoretical coding was used for the second cycle of coding. Theoretical coding is a process to group together descriptive codes that are “systematically linked with the central/core category” and provides the greatest description of the relevant phenomenon (Saldaña, 2013). In cycle one, after we analyzed all data sources using descriptive coding, different descriptive categories were created, which was the process of generating theoretical categories to describe a descriptive code from different data sources. For example, a theoretical category, “Essential contents that need to be taught for photosynthesis” included the descriptive codes “plant growth”, “mitosis”, “nutrients”, “cellular respiration and material exchanges”, “stromata and chloroplasts”, “apples growth needs energy [glucose]”. The final cycle of structural coding involved developing a visual map that graphically represents the relationships for all the theoretical categories (Figure 3). In cycle three, we used structural coding (Saldaña, 2013) and particularly looked for specific PCK connections, content knowledge, pedagogical knowledge, and knowledge of students’ preconceptions and learning difficulties in each of the theoretical categories. We used inductive reasoning for cycles one and two, and deductive reasoning was used for cycle three. Figure 3 shows an example of Jane’s specific PCK connection of how she teaches photosynthesis in her biology classroom. The visual map did not include co-teaching part of the data. The purpose of the three-cycle coding was to present detailed stories about the two teachers, and was not to compare and contrast them.

We independently coded the first cycle process to generate descriptive codes. After the first cycle coding, we shared and debriefed the coding to establish consistency in identifying descriptive codes. The process was repeated in the second and third cycle coding. We shared the coding memos and engaged discussions to examine the relationship among the theoretical categories and language that was used to describe the patterns to ensure clarity, neutrality, and consistency. A similar coder reliability process was also applied to examine the observation of the video recordings. By using the rubric, PCK classroom observation (Barendsen & Henze, 2019), an individual researcher calculated the percentage of instructional methods based on the length (minutes) that were observed in a class. Then, the researchers engaged in discussions to debrief the percentage of each class that they had recorded to establish consistency.

4. Results

The results demonstrate individual teachers’ stories and their experiences when they co-developed and co-taught the integrated STEM lessons. We used quotation marks to represent the direct quotes from the teachers.

4.1. Defining STEM Integration

Jane defined STEM integration as “when two or more subjects like math and science are taught together for a combined learning experience” (R). She believed all STEM subjects, particularly math and science, should be taught in tandem so the purpose of learning is obvious to students. By doing so, students could see where a career in technology or engineering might be in the future for them. She described STEM integration as natural to use in her class. She said, “I feel this because in biology, math is commonly used to calculate surface area (cells), population (statistics) and genetic outcomes (probability). We then use technology to retrieve and assess data, for instance running electrophoresis on specific molecules or using a computer to generate outcomes of specific genetic test-crosses” (I). She even further suggested that when a student completes a lab it is STEM integration.

Marcy defined STEM integration as “STEM is a way to integrate science, math, engineering, and technology into an interdisciplinary education course. Students learn using a hands-on, project-based approach that forms real-world connections. For me, STEM encourages educators to work together to develop cross-curriculum” (R). Marcy believed that FCS is a natural fit for STEM integration. She used the lessons that she co-teaches with Jane as an example and said, “Students learn apple variety comes from variation of genes, which is science. Using a food dehydrator brings technology into to help extend apple shelf life. Students need to decide the value and market the end-product, which is math” (I). Marcy also pointed out that she had limited knowledge about STEM integration. She described, “I am limited in how STEM can be used in the classroom. For example, I teach in a lab where sugar is substituted. I need the support of the science teacher to explain why cookies don’t turn out well with substitutes” (I).

4.2. Content Knowledge

How Jane selected what to teach is based on the state standards. Jane believed that what she does in a classroom needs to follow the state standards. She needed to “check off every single standard” and “no play[ing] around” (I). She did not teach anything outside the state standards because she did not have time to do it. Teaching science concepts outside of the state standards to her was “using a lot of time and no points” (I) because she was evaluated by how many students passed the standard test. As for Marcy, when Marcy taught her class, she focused on helping students read and write recipes, practice sanitation, and understand basic knowledge about nutrition (e.g., essential nutrients and calories). Although FCS has state standards, Marcy only picked and chose the standards she felt were most important for the students. She was not required to teach all the standards. Because she was the only FCS teacher in the school, she could teach what she wanted and “no one bothers me” (I).

Jane identified a few energy concepts in biology, such as photosynthesis, radiation, conduction, and convection. In her biology class, she taught comparative processes of respiration and photosynthesis. She stated that teaching photosynthesis is difficult because “nobody can explain what goes on in the plants” (R) and (I) and “most of my students do not work with plants.” (I) Although Jane considered photosynthesis as one of the energy concepts that she could teach, she did not choose to teach photosynthesis in the interdisciplinary project. Carbohydrates and calories were the energy contents that Jane taught in biology and tried to teach for the interdisciplinary project. She taught metabolism in her biology class about “burning it [calorie/energy] off what you take in and what you lose” (T). As for Marcy, she emphasized food can be prepared using different methods, which can change the calorific and nutritional value of the food. Marcy identified energy as calories that could be added to her teaching. She gave an example by saying, “An activity can be asking students to pick two products, a piece of apple pie and a fresh apple, and determine how many calories in these two products” (I).

The two teachers did not share too much about what they knew about food systems. They both used the examples from the interdisciplinary project that they worked on to explain how food systems (apples) make connections to the real-world, such as genetics of different apple varieties (Jane), how different varieties are crossed to produce new varieties of apples (Jane), where apples come from (Marcy), and how different varieties taste differently (Marcy).

The two teachers’ concept maps also showed differences. Jane’s concept map followed the linear structure of the state standards. For example, she listed “cellular chemistry” and noted “B.1.2 and B 1.3” (C) on the side. Below “cellular chemistry” (C), she had “macromolecules (proteins, carbs, lipids and enzymes)” (C). Then, she put asterisk marks on “*Apple nutrition (here)” and “*Oxidation (would go here)” (C) to indicate what biology contents that could be used in the interdisciplinary project. She made a note “2 weeks” (C) to indicate that she needed 2 weeks to teach the contents that were identified above. Marcy’s concept map illustrated a web structure in which all the concepts she listed interact with each other. For example, on the top, she wrote three major concepts that relate to energy, nutrition, fruit/vegetables/grains, and nutrient density. Food consumed interacted with nutrition, fruit/vegetables/grains, and nutrient density. At the bottom of her concept map, Marcy wrote “Calories 1000” and that had a line connected to “carbohydrates” and “4 calories/gram” under the fruit/vegetables/grains concept.

4.3. Pedagogical Knowledge

Because Jane has a very tight schedule that she needed to follow, she sighed, “We just kept going. It did not matter if students understood meiosis, mitosis, respiration, or photosynthesis. We just kept going” (I). She taught six classes a day and each class had about 30 students. She said, “Teaching became a game for me. I figured out how to survive in that room by myself for seven hours a day and I know how to do it” (I) and “…It’s like a repeat game. I have done this so long that I could talk to you in my sleep” (I). Moreover, Jane shared that part of the game was to navigate how the school’s administration was using strategies to hold teachers accountable to teach the curriculum aligned with the learning standards and the state standardized test. As for Marcy, how she decided the sequence of her class (and courses), and what to teach was based on the funds that the school received from the [state] Department of Education. For example, advanced nutrition had funding in the fall semester; therefore, she had to teach advanced nutrition in fall, and she moved the nutrition course to spring semester.

Jane shared that she taught content that had to align with other biology teachers. Either she needed to start at the smallest level, such as atoms, molecules, cells, and build up to an ecosystem, or vice versa. She described the routine that she used to teach her biology class. The first thing was that she needed to read the standards that she would cover to her students. Then, she asked questions, like fun facts and gimmicks. Jane called it “engaging students” (I) and (O), “keeping them up and getting their attention” (I). Next, she taught content by stating and explaining. Then, she asked some questions again. For example, after she taught photosynthesis, she asked students, “What did I just say about photosynthesis? What is the outcome?” (I) and (O). After that, she asked students to conduct a lab or do an activity. The last step was to recap and wrap up. This was the step in which Jane checked students’ understanding about the science contents after she taught them in her class.

“Follow what I do” (I) was one of the important instructional strategies that Marcy used in her class. She used many demonstrations in her class, and she expected her students to do exactly what she did. She mentioned that one of the phrases she often used in her class was “Do you remember what I did?” (I) Sometimes, she demonstrated the steps first, then asked students to follow. She repeated these steps over and over again until students could do it by themselves. Marcy also used many hands-on activities in her class because “learning by doing is the best way to learn” (I) and (R) she said. She provided food in her class as a strategy to engage her students. Based on what she believed her students are capable of, she gave students some options that they “cannot mess up” (I). For example, she did not make a cake from scratch, but from a box mix. She acknowledged that “it is alright if students make mistakes”, (I) as long as students follow the directions. Marcy wanted students to follow a step-by-step process that would likely yield a cost-effective and safe result.

4.4. Knowledge of Students’ Preconceptions and Learning Difficulties

In her pre-lesson reflection, Jane wrote about what students typically struggle with when they learn about energy transfer. She wrote, “Photosynthesis—the entire process…I have taught this for 27 years and it is always something I spend a lot of time on” (R). In her interview, she said, “They [students] don’t know what it means. They just know the word [photosynthesis]” (I). As for the food systems, Jane also considered her students to know very little. She said, “So they [students] do not understand that food is in industry. It’s a huge industry” and “It’s [the concept of food systems] a zero. Nothing!” (I).

Marcy used the word “food-driven” (I) to describe her students. She said, “They [students] like to eat, but not healthy foods (e.g., fruit or vegetables)” (I). She described her students did not have access to healthy food because they were “in poverty” (I). She also believed her students were slower readers and visual learners. Therefore, “showing” (I) them what to do was very important to teach them. In her pre-lesson reflection, Marcy wrote, “I make no assumptions of what students know” (R). Yet, she expected her students to struggle with the concept of “calories as a unit of energy” (R) and (I). She also commented that her students had “behavioral issues.”

4.5. Interdisciplinary Collaboration: STEM Integration, Content Knowledge, Pedagogical Knowledge, and Knowledge of Students’ Preconceptions and Learning Difficulties

During the brainstorming stage, the teachers used elimination methods to develop their interdisciplinary ideas. The teachers evaluated: (1) what they can or cannot do in the classroom; (2) what they know or do not know about the content; (3) how much time they had to teach the project; (4) whose classroom they would use to teach; and (5) whose standards they need to address as the decision-making process. The teachers considered the local community and how apples might be relevant to their students. The teachers shared that there are local apple orchards in the school district (T). The teachers shared that most students, if they grew up in the local area, likely went on a field trip to an apple orchard when they were in preschool (T). Therefore, the overarching problem that the teachers used to structure their integrated STEM lessons was “prevent apple waste by applying different ways to extend apple shelf life” (L), (O) and (T). Food waste and ways to extend apple shelf life, were the energy content to structure their integrated STEM lessons. They spent a lot of time researching resources and information because preventing apple waste was not something they were familiar with, nor was it something that they normally taught in their regular biology or advanced nutrition class. Although they might have decided what to teach, it could be changed at the last minute. For the teachers, interdisciplinary collaboration meant they needed to be flexible because of the additional dynamics of co-teaching.

In order to address learning standards of advanced nutrition, the teachers decided to focus the content around three points, which were: (1) introducing various type of apples (genetics and crossbreed), (2) preventing food waste (oxidation and browning), and (3) types of apples suitable for making different apple products (different cooking techniques, such as dehydrating, pickling, and baking) (L) and (T). Jane was in charge of the science content and Marcy focused on cooking techniques. Jane believed these concepts—genetics, crossbreeding, and browning—could bridge what Marcy wanted to teach. However, Jane needed to “water down” (T) the genetics and crossbreeding concepts that she normally taught in her biology class. In addition, she needed to teach oxidation, which relates to browning and enzymes, but these were concepts that she had never taught in her biology class because they are not in the state standards. As for Marcy, because it was her class, she believed that she had covered what she normally teaches in the advanced nutrition class (T). Nothing really had changed for her because she was teaching the content she was expected to teach.

The two teachers agreed hands-on activities were the center of the pedagogy used in the integrated STEM project. Jane had a total of 175 min of teaching (O). Her instruction methods included 63% of lecturing, 7% of giving instruction for students to do activities, 14% of students performing activities/labs, 3% of conclusion of students’ work, and 13% of interactive instruction. Jane acknowledged she would need more days to teach and wanted to focus on using scientific methods to conduct experiments, if this was implemented in her biology class (T). As for Marcy, she had a total of 202 min of teaching (O). Her instructional methods included 13% of lecturing, 12% of giving instruction for students to do activities, 13% of demonstrations, 40% of students performing activities/labs, 10% of conclusion of students’ work, and 12% of interactive instruction. Marcy reiterated that “nothing had changed my teaching in this collaboration” (T). The teachers followed what they believed would be the best way to teach students in their individual classroom as their interdisciplinary pedagogical knowledge.

When asked about students’ preconceptions, the teachers talked about how students had no idea where their food came from, such as burger is beef, or poultry is chicken (T). The teachers mentioned, based on their conversations with students, that students often did not eat healthy food and did not have enough food to eat (T). Therefore, both Jane and Marcy believed that food is a great way to engage students (T). They believed that students did not know different types of apples because their parents do not buy other apples besides Red Delicious, which are typically the cheapest apples (T). These preconceptions of students that Jane and Marcy held outlined their expectations about students’ learning outcomes in the interdisciplinary project. They wanted to focus their integrated STEM lessons on connecting apples to science and food waste (

Table 2. Summary of teachers’ pedagogical content knowledge and STEM integration in a co-teaching model.

	Jane	Marcy	Interdisciplinary Collaboration
Teacher’s Discipline	science/biology	CTE/family and consumer sciences
Defining STEM Integration	Two or more subjects like math and science are taught together for a combined learning experience.	A way to integrate STEM into an interdisciplinary education course. It encourages educators to work together to develop cross-curriculum.	“Prevent apple waste by applying different ways to extend apple shelf life.”
Content knowledge: Energy and food systems	Follow academic learning standards. Based on academic learning standards as the curriculum to describe energy. Identified radiation, conduction, and convection, and photosynthesis as energy concepts. She chose to teach calories for the interdisciplinary project. Did not address much about food system. Used interdisciplinary project examples to explain how food systems (apples) make connections to the real-world	Application and relevance of knowledge (standards). Follow the state funding structure. Identified energy is calories. Listed major contents that relate to calories (energy), such as nutrition, fruit, and nutrient density. Calculating calories from food connects the major energy contents. Did not address much about food system. Used interdisciplinary project examples to explain how food systems (apples) make connections to the real-world	Food waste and ways to extend apple shelf life were the energy content to structure their integrated STEM lessons. Energy is an overarching concept that helps connect what teachers need to teach. Three concepts, (1) introducing various types of apples, (2) preventing food waste, and (3) types of apples suitable for making different apple products, were used to structure their integrated STEM lesson
Pedagogical knowledge	Read the standards that she will cover to her students; teach from small scale to large scale or visa versa; need to navigate the school’s administration; asked questions, like fun facts and gimmicks, to get students to listen to her; taught content by stating and explaining; asked some questions again; conducted a lab or activity; recapped and wrapped up.	Demonstrations are important; repeated steps over and over again until students could do it by themselves. “Learning by doing” is the best way to learn. Based on her students’ abilities, she chose what her students should make in her class. It is all right to make mistakes as long as students follow the directions.	Hands-on activities were the center of the integrated STEM instructional design. Jane used most of her instruction to lecture the content, such as crossbreeding. Marcy spent the same amount of instructional time in lecturing and demonstrating. She also gave students a lot of time to do activities.
Knowledge of students’ preconceptions and difficulties	Students struggled to learn energy transfer and photosynthesis—the entire process. Students know very little about food systems.	Students are “food-driven”. Students like to eat, but not healthy foods (e.g., fruit or vegetables). “Showing” students what to do was very important. Students struggle with the concept of “calories as a unit of energy.” Students had “behavioral issues”.	Students had no knowledge about where food comes from. Students did not eat healthy food and had no access to health food. Students did not know different types of apples.

).

5. Discussion

The overarching issue that the teachers used to structure their integrated STEM lessons was “prevent apple waste by applying different ways to extend apple shelf life”. In working with each other, Jane helped introduce the science in a context of the food system using apples, and Marcy focused on helping students think about the problem of food waste and how students could design a solution to solve the problem. Although the teachers found their niches to tackle the overarching issue, the results showed that they were different in their content knowledge and pedagogical knowledge (Wang et al., 2020; Dare et al., 2019) in how they implemented STEM integration based on their own knowledge and ideas (Dewey, 1908; Schwab, 1954/1978). Teachers’ agency was likely driven by their internal epistemological beliefs or external expectations to teach to state and administrative expectations (Wang et al., 2020). Jane was driven by teaching learning standards and helped students learn the science content that students would be tested on with the state’s standardized tests. Marcy taught courses that the school district received funding from the state for teaching CTE courses. Although she used learning standards, she also thought about what was important for students to know and how to use skills in the real-world. When the teachers co-taught their lessons, they prioritized their instructional goals of teaching learning standards and objectives, and content knowledge and skills based on their individual PCK (Wang et al., 2020; Herschbach, 2011) in which they were most comfortable that were loosely aligned with solving the overarching problem with a specifically designed solution.

Jane conceptualized energy as a crosscutting concept (NGSS Leader States, 2013) that she could add into her teaching in several ways. Marcy considered energy as an important concept in her nutrition class. In working with each other, the two teachers tried to tie a very specific form of energy, which were nutrition and calories, into their lessons during the planning stage. This may have been because energy is an abstract idea (Millar, 2014), and energy was interpreted in different forms by the two teachers (i.e., photosynthesis by the science teacher and calories by the FCS teacher; Chabalengula et al., 2012; Opitz et al., 2015). Although they had an overarching problem that concerns the energy embedded in wasted food, food waste as energy wasted was not the critical content that they taught in their integrated STEM lessons. The teachers explained how their individual content areas related to energy concepts, yet their students were not explicitly taught about energy conservation in solving the complex food systems problem. In order to meaningfully integrate STEM subjects, teachers should help students to apply the to-be-learned STEM content to solve problems (Wang & Knobloch, 2018). The integrated STEM lessons that the two teachers developed did not achieve that.

T. Park et al.’s (2017) findings suggest CTE (also known as, vocational) and science teachers who collaborated increased their level of respect for the other content area and collaborating on an integrated project made them think differently about the way they taught. In this study, Jane had a sequence that was similar to guided/structured inquiry: (1) teaser; (2) content; (3) activity; and (4) debrief and wrap-up. Jane’s emphasis on teaching to state learning standards supported that biology teachers conceptualized integrated STEM teaching as being more aligned with content integration (Moore et al., 2014). Marcy followed an order of key steps using demonstration to help students to make edible and safe food products, such as she often asked students to follow a recipe. When they co-taught the integrated STEM lessons, although they appreciated each other’s different teaching styles, they did not change how they taught as if they still teach in their individual class in a co-teaching model. The evidence the teachers shared reflected both knowledge and practices, which aligns with the theoretical assumptions of PCK (Gess-Newsome, 2015; Gess-Newsome et al., 2019). Moreover, this supported the premise that teacher professional identity (Sachs, 2005) plays a role as active agents in planning, and instruction–science is viewed as foundational and formal knowledge, which is aligned with standardized tests and disciplinary structure and rules; whereas, FCS (i.e., CTE) is considered a practical subject that applies science concepts (Wang & Knobloch, 2023; Herschbach, 2011). The two teachers had different pedagogical knowledge, and they demonstrated how their disciplinary thinking and professional identity informed their pedagogical knowledge and decision-making (Wang & Knobloch, 2023).

Jane reported more trade-offs regarding how she would have taught her content to meet the learning standards, but she was flexible because she was teaching in the FCS course. We acknowledge teachers likely have more flexibility when integrating academics into CTE courses, which aligned with T. Park et al.’s (2017, p. 204) recommendation that “integration should begin with the CTE curricula, and not with academics.” Further, Park and his colleagues stated CTE teachers have better results when “academics remain authentic to workplace problems and solutions” (p. 204). Teachers can be creative and flexible about the to-be-learned STEM content (Rojewski & Hill, 2017), but their integrated STEM instructional design were informed by their disciplinary thinking and professional identities.

Knowledge about students is one important component of PCK. Jane and Marcy both assumed that their students knew nothing about the content of energy and food systems. They believed their students were not knowledgeable about where food comes from (Mercier, 2015). Assuming students know nothing about the content was also documented in other PCK study (Mthethwa-Kunene et al., 2015). The two teachers acknowledged their students lived in food and nutritionally insecure communities because of poverty. In the U.S., 13.5% (18.0 million households) were food insecure in 2023 (Rabbitt et al., 2024). Rabbitt et al. defined food insecurity as households that “had difficulty at some time during the year providing enough food for all their members because of a lack of resources” (p. iii). The teachers also reported cultural differences played a role in food preferences (Enriquez & Archila-Godinez, 2022). For example, the students narrowed down their possible solution was to purchase a dehydrator and dry slices of apples. However, the students were not familiar with dried apples, and they did not like the taste and texture. Then, the students decided they would make apple muffins as their solution, and they enjoyed the flavor and texture of the apple muffins. The integrated STEM lessons that the two teachers developed had a big emphasis, which is introducing a health food, apples, to their students. In this study, when developing the integrated STEM lessons, knowledge of students’ preconceptions did not relate to students’ learning difficulties but connected to what students needed the most in their daily learning. This is aligned with another research study that food system STEM projects help students make local cultural connections to their families and communities (Thies et al., 2024).

6. Limitations

Although the two teachers during the TDP were introduced to the definition and instructional design of STEM integration from the researchers and STEM experts, we did not restrict them to use the same definition and instructional design. We purposefully wanted to explore teachers’ PCK, after they formed an interdisciplinary team, and how they co-developed and co-taught integrated STEM lessons. What teachers considered as integrated STEM teaching and interdisciplinarity learning might not be the same as the researchers. This was a struggle with the study. On the one hand, we wanted to make minimal interventions when we studied teachers’ PCK in a co-teaching model. On the other hand, the final product (lessons and instruction) might not meet the expectations of STEM integration that reach interdisciplinary learning. Although from the teachers’ perspective that they had co-developed and co-taught integrated STEM lessons, we acknowledged experts from the field of STEM integration might argue that a co-teaching model helped teachers scaffold their PCK to be more integrated and interdisciplinary. In addition, this qualitative research focused on two teachers’ experiences. Therefore, it cannot be generalized to a larger population, but serves as examples that may be transferable.

7. Conclusions

We explored what interdisciplinary collaboration of developing integrated STEM lessons and instruction aligned with a cross-cutting theme (i.e., energy conservation in the context of a food system) means through the lens of PCK in a co-teaching model. The results showed that developing integrated STEM knowledge and skills is a developmental process, which is not a concept that naturally dwells in teachers’ daily teaching. Our findings suggested that experienced teachers retained their pedagogical knowledge during interdisciplinary collaboration. During interdisciplinary collaboration, teachers leverage their existing pedagogical knowledge, which is shaped by their disciplinary thinking and professional identities (Wang & Knobloch, 2023; Sachs, 2005), to develop integrated STEM lessons. As the result, when they co-develop and co-teach integrated STEM lessons, the pedagogical knowledge from individual disciplines flavors the integrated STEM learning experience. Therefore, co-developing and co-teaching an integrated STEM model is more difficult than an individual integrated STEM model because teachers need to take time to develop trust and understand each other’s disciplinary perspectives to create learning experiences that engage students in interdisciplinary and transdisciplinary ways.

Although expectations of teacher change exist, the first time implementing the integrated STEM lessons will not likely change teachers’ PCK. It was difficult for the teachers to decompartmentalize disciplinary boundaries to help students make interdisciplinary connections (Moore et al., 2020; National Research Council [NRC], 2014; National Research Council [NRC], 2012; National Science & Technology Council [NSTC], 2018). Teachers who engage in new teaching innovations may be willing to work through the process to improve how they teach students. However, the novelty and first-time teaching collaboratively cloud challenge teachers’ understanding and development of co-teaching integrated STEM instruction. Further research is needed to understand the developmental process of teacher change. Teachers may change their PCK by working collaboratively with teachers from other disciplines, but this may take multiple successions and years for teachers to understand and develop their collaborative PCK. Further studies focused on bridging the chasm between academic and CTE will provide insights in better understanding how integrating STEM in CTE will prepare students for college and the workforce (Rojewski & Hill, 2017). More research is needed to understand the nuances and how teachers in different disciplines, in different stages of development, and in different collaborative arrangements develop their PCK through integrated STEM instruction.