A Systematic Review of Effective Instructional Interventions in Supporting Kindergarten English Learners’ English Oral Language Development

Abstract

In this systematic review, we explore research on effective interventions and approaches targeting kindergarten English Learners’ (EL) English oral language development. A total of seven studies met the inclusion criteria. The review summarizes the common characteristics of a practical intervention that could be applied to support kindergarten Els’ English oral language development. In addition, we summarize the measurements that were applied to measure Els’ oral language proficiency in English. However, future research using a longitudinal design is needed to determine the long-term impact of quality intervention on ELs’, especially those with limited resources, oral language development.

1. Introduction

English Learners (ELs) account for the fastest growing population in U.S. public schools, with an increase from 4.5 million (9.2%) in fall 2010 to 5.0 million (10.2%) in fall 2018 [1]. NCES (2021) further reported that in fall 2015, there was a larger proportion of public-school students who were identified as ELs at lower grade levels (e.g., 15.1% in kindergarten) as compared to those in upper grades (e.g., 8.9% in Grade 6 and 7.4% in Grade 8). Regarding geographic concentration, the state of California reported the highest percentage of EL enrollment at 19.4%, followed by Texas at 18.7% (NCES, 2021). In comparison to their non-EL counterparts, ELs tend to be at higher risk of performing poorly on various academic disciplines, such as math and reading (U.S. Department of Education, 2017). For example, in 2019, ELs performed significantly lower in National Assessment of Educational Progress (NAEP) reading at 4th grade, 33 points lower than the average score of their non-EL peers [1]. Furthermore, ELs have a significantly lower high school 4-year graduation rate [2]. These ELs are equipped with limited academic English proficiency, which presents a great challenge for researchers and practitioners as to how to better support ELs with quality instruction so as to improve their academic performance and to be compliant with the Every Student Succeed Act (ESEA; [3]). Additionally, it is a major challenge for schools to prepare ELs with native-like English proficiency to make academic achievement possible under the pressure of the ESSA, where there is a shift toward accountability policies for schools [3,4].

1.1. Kindergarten ELs’ Oral Language Development

Sustainable development of early language education plays a significant role in students’ academic life [5]. Ways to sustain oral language development, one of the critical indicators of language education, should thus be emphasized and explored. It is well documented in previous studies that there is a positive relationship between ELs’ oral language proficiency and their reading performance [6,7,8,9,10,11,12]. In addition, oral English proficiency is associated with subsequent English literacy skills for young ELs, which also impact later school success [13,14,15]. The development of ELs’ oral language has a sustainable impact on their academic success at school and professional development in the future [16,17,18]). However, despite the important role that oral language development plays in ELs’ academic lives, limited empirical studies have been conducted to explore ELs’ oral language development [15,16], and there is a need for direct instructional support for ELs’ oral language development [15]. Moreover, it was suggested that, besides the concerted effort to develop ELs’ oral language performance at early grade levels, sustained and quality support is required to enhance their later academic performance [19]. However, limited studies have been conducted to follow up ELs’ sustainable development in language learning.

The definition of oral language proficiency is not limited to listening and speaking; it involves multiple elements that might in turn impact students’ future academic learning [13,20,21]. These elements include acquisition of academic and domain-specific vocabulary, phonological awareness of the sounds of a language, morphological knowledge of word parts and forms, syntactical knowledge of the grammatical rules, pragmatic knowledge of the social rules, and discourse knowledge to develop oral communication [2].

The early years of life are critical to children’s lifelong sustainable development as their early education experience set the stage for future academic success [22]. It has been indicated that children’s early language development occurs mainly through oral and listening experience [23,24], therefore, it is important to explore approaches to support ELs’ oral language development in the early school years. The formal schooling of oral language begins in the kindergarten year, which has a significant and long-term effect on children’s current and future academic success [25,26,27] because, during that year, children learn and develop memory, basic math, and literacy skills, and build fundamental science knowledge [26]. A growing body of research has been conducted to investigate issues related to kindergarten ELs’ oral language proficiency, such as language interaction and oral language development [28,29], the impact of school or home factor on oral English proficiency [9,30]), and the connection between Els’ first and second oral language development [31]. These studies have suggested that ELs’ oral English proficiency at an early age has a critical impact on their subsequent academic performance, which further underscores the need for effective oral language instruction to better prepare ELs.

Although positive findings on oral language among kindergarten ELs have been reported from interventional research (e.g., [32,33,34]), after searching, we found that no study has comprehensively and systematically synthesized the literature on this topic. What is available in the literature includes meta-analyses and research syntheses on program effectiveness with a special focus on ELs’ reading achievement (e.g., [35,36,37]). The review performed by Marulis and Neuman [38] on the effectiveness of vocabulary intervention on pre-kindergarten and kindergarten children’s oral language development did not focus on ELs and contained insufficient information on interventions and programs that could be utilized to support the development of ELs’ oral language proficiency. Therefore, the purpose of this study is to systematically review studies that implemented effective oral interventions on kindergarten ELs. In an era with increased school accountability, such a review is particularly timely.

1.2. Definition of ELs and Types of Bilingual Program

The term ‘English learners’ describes students who are “in the process of actively acquiring English, and whose primary language is one other than English” [39] (p. 7). In the United States, under the Every Student Succeeds Act, ELs are mandated to take annual assessment on their English language proficiency, and state governments are responsible for providing accommodations for these students on the assessments [40].

There are two commonly adopted bilingual models serving ELs: Transitional Bilingual Education (TBE) and the Dual Language (DL) Immersion program [41]. In the TBE model, both students’ native language and English are applied as mediums of instruction during a transitional period to support learners whose L1 is not English [42]. The primary goal of this model is to gradually diminish the use of learners’ primary language and mainstream them into an English-only instruction classroom [42]. TBE provides both an early exit and a late exit model; the first model provides some initial instruction in students’ L1 and expects L1 instruction to phase out rapidly by Grade 2, while the latter model usually serves ELs from kindergarten through Grade 6, and students receive 40% of L1 instruction time [41]. In a DL immersion program, students are served in both English and another language with no intention to diminish the use of primary language. There are two forms of DL programs: the one-way model and the two-way model. The DL one-way model is designed for ELs to participate with their first language applied as instructional language, and English is taught as a second language [43]. The DL two-way model allows both ELs and native English speakers to participate and receive instruction in two languages [44].

The goal of this study was to systematically review studies addressing the development of kindergarten ELs’ oral language proficiency through instructional intervention. In this review, we address the following research questions:

• What are the characteristics of the EL students involved in the studies (i.e., native language, location, SES background)?
• What bilingual program types were used in these studies?
• What was the impact of instructional intervention on kindergarten ELs’ oral language development?
• What instruments were applied to measure ELs’ English oral language proficiency?

2. Method

2.1. Selection Criteria

According to Gough et al. [45], a systematic review is “a review of the research literature using systematic and explicit accountable methods” (p. 261). It serves as a functional approach to critically synthesize and organize collected research material [46]. We adopted features described by Cooper et al. [47] when conducting the systematic review in the current study. In order to capture all relevant studies related to the development of kindergarten ELs’ oral language development, we collaborated with a professional librarian, whose responsibilities included conducting literature reviews in the field of health and medical science [48]. Inclusion criteria for screening include the following:

• Research participants included ELs in kindergarten;
• Research outcomes of the study included English oral language development;
• Research involved an intervention that was aimed at improving the quality of instruction, which led to oral language development;
• Intervention studies included pre- and post-assessment;
• Research was conducted in the United States;
• Studies were peer-reviewed quantitative studies.

In addition to the inclusion criteria, exclusion criteria were also applied to select studies that best fit the research purpose. Excluded studies were:

• Studies using kindergarten students’ oral language outcome as a baseline or predictor of later reading or writing performance, which meant there was no report on their performance at the kindergarten year independently;
• Studies including outcomes other than the six components of oral language proficiency outlined by Fisher and Frey [2];
• Studies conducted to analyze the psychometrician characteristic of an instrument designed to measure oral language development of kindergarten ELs;
• Studies conducted in other English-speaking countries with ELs;
• Master’s theses and doctoral dissertations.

2.2. Location and Selection of Studies

In an attempt to locate every study that might meet the inclusion criteria, a comprehensive and systematic search of articles written between January 2000 and October 2018 was conducted. Electronic searches were made in the following databases: ERIC, Linguistics and Language Behavior Abstracts, Academic Search Ultimate, Education Source, and Psyco Info. A primary search was conducted in each database based on different combinations of keywords. Descriptors included: English learner (EL), English language learner (ELL), English as second language (ESL), limited English speaking, English oral language development, oral language proficiency, verbal communication, and kindergarten. As a supplementary measure, we also searched targeted educational journals, including: Bilingual Research Journal, Elementary School Journal, Journal of Multilingual & Multicultural Development, Language and Education, and Early Childhood Research. An initial search resulted in 202 bibliographic entries. After being imported into Rayyan [49] for deletion due to duplication, 93 duplicate studies were removed. There were 109 unique studies. Each article was indexed by searching primary keywords and was assigned to two raters, myself and an enlisted doctoral student studying educational psychology, for initial screening on title and abstract. We worked independently to review the titles, abstracts, and keywords of these articles for possible inclusion or exclusion by applying the selection criteria stated above. Eighty-six studies were excluded during the process for the following reasons: the study did not focus on oral language development, the study was a non-quantitative study, the study was not conducted in the United States, the study’s participants were not kindergarten children, or the study was a psychometric analysis of an instrument focused on kindergarten ELs’ English oral development. The remaining 23 studies were downloaded for further analysis. We further applied exclusion criteria to disregard 16 studies, resulting in 7 empirical studies (

Table 1. List of studies included for final in-depth review.

Author	Journal	Title
Rebecca Silverman	The Elementary School Journal	A Comparison of Three Methods of Vocabulary Instruction during Read-Alouds in Kindergarten
Fuhui Tong, Rafael Lara-Alecio, Beverly Irby, Patricia Mathes, and Oi-man Kwok	American Educational Research Journal	Accelerating Early Academic Oral English Development in Transitional Bilingual and Structured English Immersion Programs
Fuhui Tong, Beverly Irby, Rafael Lara-Alecio, and Patricia Mathes	Hispanic Journal of Behavioral Sciences	English and Spanish Acquisition by Hispanic Second Graders in Developmental Bilingual Programs: A Three-Year Longitudinal Randomized Study
Fuhui Tong, Beverly Irby, Rafael Lara-Alecio, Myeongsun Yoon, and Patricia Mathes	The Elementary School Journal	Hispanic English Learners’ Responses to Longitudinal English Instructional Intervention and the Effect of Gender: A Multilevel Analysis
Saunders William, Barbara Foorman, and Coleen Carlson	The Elementary School Journal	Is a Separate Block of Time for Oral English Language Development in Programs for English Learners Needed?
Pamela Spycher	The Elementary School Journal	Learning Academic Language through Science in Two Linguistically Diverse Kindergarten Classes
Youb Kim	The Modern Language Journal	The Effects of Integrated Language-Based Instruction in Elementary ESL Learning

). We present a flowchart in Figure 1 to outline the decision-making process following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA; [46]).

3. Results

A total of seven studies, including approximately 2602 kindergarten children, met the inclusion criteria for this review exploring the impact of instructional intervention on the development of kindergarten ELs’ oral English proficiency. Results are presented in four sections that address the research questions: participant characteristics of the studies, types of bilingual models, interventions designed to improve ELs’ oral language development, and instruments applied to measure students’ oral language proficiency.

3.1. Participants

Among the seven studies, five exclusively focused on ELs. One included both ELs (38%) and non-ELs (i.e., [50]), which reported English language status as a non-significant covariate on ELs’ oral vocabulary learning [50]. Another included both ELs (54%) and non-ELs [33] and reported that there was no significant difference found between ELs and non-ELs regarding the number of words they knew in both treatment and control conditions. The majority of ELs in these studies were from low socioeconomic status (SES) backgrounds, which was determined by whether they qualified for the free or reduced lunch program. We also found that participants in all of the studies were native Spanish speakers, except the study by [32], in which two participants spoke Chinese and Korean as their first language. Five studies were conducted in California and Texas. The other two studies [32,50]) did not provide specific information on the location of their studies.

3.2. Program Types

Among the seven studies, four reported the types of bilingual programs students were enrolled in, with one describing an English immersion program [51] and the other three studies involving multiple types of bilingual programs, such as transitional bilingual programs [34,52,53], immersion programs [34,51,52], maintenance programs [52,53], and a dual-language program (i.e., [52]).

Detail description of bilingual program types were provided in three of the studies [34,51,53]. For example, Tong et al. [53] reported that their intervention was conducted in the 70/30 (Spanish/English) developmental bilingual education program at kindergarten. Spanish was applied as the medium of instruction in all content areas including language, arts, math, science, and social studies. Tong et al. [51] also explained that the students in the study were placed in a structured English immersion program, where all instruction was delivered in English. Saunders et al. [52] only reported the quantity of participating schools classified into one of the four program types; no detailed information of the implementation of these programs were provided.

3.3. Intervention

In this section, we categorize the seven studies into three general groups based on the types of intervention implemented in the studies: language-based interventions, oral vocabulary-based interventions, and whole-school interventions.

3.3.1. Language-Based Intervention

Kim [32] examined two language-based programs in developing young learners’ oral language proficiency with two kindergarten ELs in a Midwestern state. The intervention duration was 10 weeks, and both participants received integrated (oral + written) language-based and oral language-based interventions twice, in different orders. A total of four themes were included in the instruction: food, places we live, clothing, and transportation. Integrated language-based intervention consisted of four steps: (a) teacher reading a story or pictures based on the theme; (b) pre-journal writing activity to develop students’ oral language development and writing skills; (c) students reading their personal journal by themselves or with teacher; and (d) a review of words and sentences covered in the session. As for the oral language-based instruction, reading and writing were not involved in this type of intervention. Three steps were implemented in oral-language based instruction: (a) students listening to teachers’ explanation of a story or pictures while looking at the pictures; (b) oral interaction with teacher on game or conversation where the main idea of the story was discussed; and (c) oral review of what was covered in the session. Each student received an intervention of 12 instructional sessions based on two themes for each type of instruction. A 30-min mini lesson and daily pre- and post-assessment of oral language use was implemented for every instructional session with the purposes of expanding learners’ vocabulary in the theme and helping them use complete sentence with more than one word. Results of the study suggested that integrated oral + written language instruction is more beneficial for students’ oral language development compared to oral language instruction only. It further indicated that literacy should be taken into consideration at the beginning of ELs’ instruction.

3.3.2. Oral Vocabulary Intervention

Spycher [33] examined the effectiveness of a vocabulary intervention that targeted young learners’ English oral language development. The study lasted over 5 weeks with 39 kindergarten students in two self-contained science classrooms with the same teacher in an urban school of California. The control class received implicit instruction with exposure to academic vocabulary through regular science instruction and teacher read-aloud. The treatment class received intentional instructional intervention with explicit instruction on academic vocabulary, such as choral reading and teacher-provided student-friendly definitions in addition to traditional science instruction. Students in intentional instructional class spent 20 to 25 min each day learning three to six academic words based on the science lesson during a week. As the treatment class received extra instruction on their vocabulary lessons, the control class engaged in other regular classroom activities. The selection of words taught in the treatment class followed the “three-tier” concept by Beck, McKeown, and Kucan [54], which categorized words as tier 1 or basic everyday word, tier 2 or high-utility academic words, and tier 3 or discipline-bound academic words. Coaching was also applied to support the teacher before the implementation of the intervention. The findings of the study demonstrated that students in the intervention class recognized more target vocabulary and could elaborate more on scientific concepts compared to their control peers.

3.3.3. English Language and Literacy Acquisition (ELLA)

Three closely related studies retrieved from a large 4-year longitudinal randomized research project, ELLA, were included in this review [34,51,53]. To be more specific, kindergarten students in project ELLA received 75 min of an ESL block every day, including 25 min allocated to Story Retelling and higher-order thinking for English Literacy and Language Acquisition (STELLA; [55]), 10 min on teacher conducted Academic Oral Language (AOL), and 40 min to Santillana Intensive English, which is a research-based instruction in teaching Spanish speaker content in kindergarten and first grade [56]. In the first study, Tong et al. [34] examined the effectiveness of the 2-year oral English intervention from the beginning of kindergarten to the end of first grade. Participants were 534 ELs from 23 schools in TBE and Structured English Immersion (SEI) programs. The findings of the study suggested that students in both program types made significantly positive growth in their English oral language. Further, students receiving enhanced instruction developed at a faster rate than those with typical instruction. In the second study [51], researchers followed ELs who were enrolled in SEI programs from kindergarten to the end of second grade. A total of 339 students participated in the study in kindergarten. Based on the descriptive statistics, at the end of kindergarten, male students under ELLA conditions numerically outperformed their peers in the control condition at phonological skills and oral proficiency. It was further suggested that girls develop faster than boys in the area of phonological skills. A parallel study was conducted by the research team to track students enrolled in TBE programs K-2 [53]. A total of 19 schools were randomly assigned to ELLA treatment (N = 10) or control (N = 9) conditions. Students in the treatment condition received an enhanced developmental bilingual education program with a 70% Spanish and 30% English instruction model, whereas those in the control condition received a traditional bilingual model with 80% Spanish and 20% English. The initial sample included 502 students, and by the end of the year there were 489 students in the project. Tong [53] found that students under ELLA conditions outperformed their counterparts in the control conditions in the area of phonological awareness after the first year of intervention.

Silverman [50] compared the effectiveness of three vocabulary teaching approaches: (a) contextual instruction; (b) analytical instruction; and (c) anchored instruction among 94 children. Developed based on the findings of Teale and Martinez [57] and Dickinson and Smith [58], the contextual instruction method provides a curriculum with all instructional time devoted to fostering the discussion of new words, learning from stories and in relation to students’ personal experiences. The analytical method was designed based on the studies of Dickinson and Smith [58] and Beck and McKeown [59]. In the analytical curriculum, children first learn target words through discussion of the context of the words and their personal experience, then they analyze these words by applying them to various other contexts. Anchored instruction was developed based on Beck and McKeown [59] and Juel, et al., [60]. The technique includes phonological and orthographic aspects of words. In anchored curriculum, students need not only discuss target words in context and in relation to personal experience, but they must also compare and contrast words and further attend to the sounds and spelling of target words. The findings suggested that anchored and analytical instruction are more effective in terms of improving children’s oral vocabulary learning than contextual instruction.

3.3.4. Whole-School Interventions

Saunders et al. [52] investigated the effectiveness of separate English language development (ELD) into a separate instruction block. A total of 35 schools with 85 kindergarten classrooms serving 1399 students participated in the study. Students in each classroom received either oral English language development through a separate ELD or regular reading/language arts instructional block without a separate ELD. Classroom observation was conducted to monitor the process of ELD or non-ELD classrooms. It was found in the study that ELs benefited more from classrooms with ELD blocks because instructors provided them with more opportunities to engage in oral language and literacy activities. It was found that students in classrooms with a separate ELD block demonstrated a modest but significantly higher performance regarding oral language development than those without.

3.4. Measurement

This section elaborates on measurements that were applied to measure ELs’ oral language proficiency in English in the studies including standardized assessment as well as researcher-developed instruments.

The Woodcock Language Proficiency Battery—Revised (WLPB—R; [61]) was the most commonly administered instrument to measure students’ oral language development in the studies reviewed. This is a standardized instrument with both English and Spanish forms assessing a broad range of proficiency in oral language, language comprehension, reading, and writing. The English norms of the WLPB—R were obtained from 6359 native English-speaking subjects from age 2 to 99 years, including 3245 students in K-12. Construct, content, and concurrent validity information were provided in the test manual [61]. Students’ oral language skills can be assessed with five subtests: picture vocabulary, listening comprehension, oral vocabulary, memory for sentences, listening comprehension, and verbal analogies. In the picture vocabulary subtest, based on the guidance of the examiner, test takers need to match words with pictures and pronounce the words when displaying a picture. This is an expressive semantic task to measure students’ vocabulary knowledge. In the listening comprehension subtest, examiners read a passage and test takers listen to the passage and fill in the single missing word at the end of the passage. In the verbal analogies test, test takers need to provide verbal answers to questions that involve logical relationships. Cognitive ability was also assessed through the verbal analogies subtest in addition to oral language proficiency. Through the review process, we found that four out of the seven studies used picture vocabulary and listening comprehension subtests [34,51,52,53].

The Woodcock-Munoz Language Survey (WMLS—R; [62]) was also included in one of the studies [32]. It is a norm-referenced instrument with sets of tests to examine students’ English and Spanish language proficiency across multiple domains, including oral language, language comprehension, and reading and writing. The English norms of the WMLS—R were obtained from 8818 participants from age 2 to over 90. Each form of WMLS—R consists of seven tests, and the combination of these tests form clusters to measure different domains. Three clusters could be applied to evaluate students’ oral language development, including an oral language cluster, an oral expression cluster, and an oral language-total cluster. The oral language cluster briefly measures listening and speaking skills and comprises two subtests: picture vocabulary and verbal analogies. The oral expression cluster measures expressive vocabulary, language comprehension and development, and memory, and it comprises two subtests: picture vocabulary and story recall. The oral language-total cluster measures a wide range of language competency and comprises four subtests: picture vocabulary, verbal analogies, understanding directions, and story recall.

The Test of Oral Language Development P:3 (TOLD; [63]) is another standardized norm-referenced instrument that measures children’s receptive and expressive spoken language competence. Silverman [50] applied TOLD to measure students’ general vocabulary knowledge with three core subtests: picture vocabulary, relational vocabulary, and oral vocabulary. Picture vocabulary is a semantic subtest that contains 34 items to assess the extent to which the test taker understands the meanings of oral English words. Test takers respond by pointing to the pictures that represent the meaning of the word spoken by the examiner. Relational vocabulary is a semantic subtest that consists of 34 items to measure students’ understanding of two stimulus words. Test takers first understand the meaning of the spoken words, then recognize the semantic category of the words, and orally explain the relationship between the words. Oral vocabulary is another semantic subtest that is given by the examiner, with 38 items to assess a student’s ability to explain the meaning of common English words.

Finally, Comprehensive Test of Phonological Processing (CTOPP) is a norm-referenced instrument used to measure students’ ability in phonological awareness, memory, and rapid naming. Norming of the instrument was based on a sample of 1636 students ranging from 5 to 24 years; half the participants were elementary school students. CTOPP contains 13 subtests, and four of them were administered in Tong et al.’s [53] study: blending phonemes into words, rapid object naming, rapid letter naming, and segmenting words. Blending phonemes into words is a 20-item subtest that requires test takers to first listen to sounds produced on an audio cassette recording and then combine the string of phonemic sounds into words. Rapid object naming contains 72 items, in which test takers need to name a series of six objects that are randomly displayed in a 4 × 9 table as quickly as possible. Rapid letter naming is a 72-item subtest that requires test takers to recognize a string of six letters that display randomly in a 4 × 9 table. Segmenting words contains 20 items and is a supplemental subtest that requires test takers to identify target words separated into phonemes.

Researcher-Developed Instrument

In addition to the standardized assessments reported in the seven studies, researchers also relied on self-developed instruments to collect outcomes. For example, Spycher [33] developed the Emergent Science Vocabulary Assessment (ESVA), an individually-administered picture test to measure students’ oral language through their receptive vocabulary knowledge. The design of ESVA used the Peabody Picture Vocabulary Test—Third Edition (PPVT—III; [64]) as a model with 20 academic vocabulary words that were taught during the intervention. Validity and reliability of the instrument were examined through a pilot study, which yielded a good fit for measuring students’ target vocabulary knowledge. In addition to the 20 words retrieved from the intervention, another 10 words that students were more familiar with were also included in the ESVA. During the assessment, students were shown a 2 × 2 table containing four color photographs. Students were asked to follow the tester’s instructions, such as pointing to the target word and choosing the photograph that represented the word. The other three distracting choices were appealing to the students, semantically related, and phonologically related to the target word.

Kim [32] used a daily picture descriptions informal test before and after the intervention to evaluate the effect of treatment intervention on students’ oral language development. Each daily picture description task was administered for 2 min and 50 s. For each theme, students were presented with displays of four pictures. Students were required to follow one of the general prompts used for daily picture description tasks, including “tell me what you see in this picture,” “please tell me what you see in this picture,” or “can you tell me what you see in this picture?” The four pictures displayed under one theme were selected from three categories: (a) defining moments [65], which included a real life picture from a commercial calendar; (b) Oxford picture dictionary for kids [66], two colorful illustrations were selected from this commercially developed picture book for ESL students; and (c) pictures composition [67], black-and-white, two-tone illustration pictures were chosen from this picture book, which was also developed for ESL students to guide composition. The scoring of this daily assessment was additive and consisted of the following five areas: total number of words students used; pragmatic acceptability—students’ appropriate response to teachers’ questions; semantic acceptability—students’ accurate description of the picture; syntactic acceptability—students’ use grammatically appropriate sentences; and absence of promoting—students’ reaction to general prompts during daily tasks. Finally, Silverman [50] designed the researcher vocabulary assessment (RVA) to measure students’ word knowledge two weeks prior to and directly after the intervention. This assessment consisted of two orally administered subtests: a picture subtest and an oral vocabulary measure. For the receptive picture subtest, students needed to choose one out of four pictures that best represented the target word given by the tester. For the expressive oral subtest, students were asked to define the target word orally. The total possible score for each subtest was 30, and for each correct response, one point was given to the student. Before students took the actual assessment, practice items were provided to students to make sure they understood the task.

4. Discussion

Existing literature has confirmed the importance of early oral language proficiency, which can significantly predict ELs’ subsequent reading or writing performance at upper grade levels [68,69,70,71]. In this systematic review, we have explored multiple forms of intervention that were aimed at improving kindergarten ELs’ oral language development and instruments that have been used to measure oral skills. The discussion is presented in the order of the research questions.

With over 90% of participants from either California or Texas State, the findings of this review are consistent with the distribution of ELs in the United States. According to NCES [1], by fall 2017, California reported the highest percentage of ELs (19.2%) enrolled in public schools, followed by Texas (18.0%). However, it must be noted that there is a significant number of ELs in other states. Future research should consider investigating ELs’ language proficiency in other states that have had a steady increases in their EL population and help these students to make academic progress. Moreover, other than Kim [32], who examined students whose native languages were Chinese and Vietnamese, the rest of the participants were Spanish-speaking ELs. It was reported by NCES [1] that though Spanish was the most widely spoken home language of ELs in fall 2015, Arabic, Chinese, and Vietnamese were also common home language of ELs. Future studies should consider examining the oral language performance of ELs among more diverse native language backgrounds to identify differences or similarities.

The review of the studies suggest that there were effective intervention programs in improving kindergarten ELs’ oral outcomes. Some of these could be adopted broadly among a large group of students. For example, a separate ELD block, a whole-school approach with students receive oral English language development through a separate ELD instead of a regular reading instructional block, proved to be successful [52]. Three forms of vocabulary interventions had a positive impact on ELs: instructional intervention, analytical instruction, and anchored instruction. These interventions are whole-class or whole-school interventions that could be adopted to serve schools with a high concentration of ELs. Across these promising interventions, several common components were found to be effective. First, student–teacher interaction plays an important role in most of the interventions. Successful models include teachers who provide students with more opportunities to speak and use English to discuss their opinions. For example, in an anchored instruction curriculum, students are required to discuss the target word under the context and relate it to their personal experience. Secondly, most of the interventions were designed as an independent, separate English learning block. In these interventions, ELs were provided with an extra language learning period to acquire the language. For example, ELLA offered students with a direct and structured English intervention implemented during the ESL block with multiple components. Additionally, teacher training and professional development were implemented in most of the studies. Project ELLA provided teachers and paraprofessionals with bi-weekly professional development workshops [34]. Silverman [50] also provided individual training to teachers. Saunders et al. [52] agreed with the importance of providing teachers with professional development regarding academic language instruction.

The reviewed studies suggested that the quality of intervention is as important as the language of instruction, which impacts ELs’ learning outcomes [35,72]. Students who are identified as ELs were provided with opportunities to participate in language assistance programs [73]. The needs of Els varies from state to state; in some states, bilingual education programs are required, while in other states these programs are developed as needed [74]. For example, in Texas, a full opportunity to participate in English as a Second Language (ESL) or bilingual education program shall be provided for any students who speaks a language other than English as their primary language and who are identified as EL [75].

However, due to policy issues and limited resources, not all states can provide qualified dual language program to support ELs [74]. Although the use of ELs’ native language in dual language programs is beneficial for ELs [76,77], districts and schools face a variety of challenges implementing these programs, including a shortage of qualified teachers and the additional costs of program development [74]. Based on the available resources and the current context, researchers and schools should focus on improving the quality of instruction to foster ELs’ academic learning. There are several common features found in the reviewed studies that are beneficial for ELs’ oral language development. Schools and teachers should incorporate these features into their instruction to better serve the academic and language needs of ELs.

Among the instruments implemented in the reviewed studies, there are generally two categories: self-designed instruments and widely adopted standardized tests. The most commonly applied standardized instrument in the reviewed studies was WLPB—R, which was designed to measure a broad range of domains. Based on the content of the intervention, researchers also designed informal tests to measure students’ oral language proficiency. Generally, picture tests, a type of assessment that require students to make relationships between spoken vocabulary and images, was the most-used testing form. Compared to standardized tests, researcher developed instruments had less generalizability and provided little information regarding reliability and validity. For future research, other than standardized tests and researcher-developed instrument, state level high-stakes tests should also be evaluated as appropriate instruments to measure students’ performance of various domains.

In addition, in the review we also discovered other elements regarding kindergarten ELs’ oral language development. First, it is well documented in previous literature that effective professional development can develop teachers’ pedagogical behavior and improve their instructional approach for ELs [78,79,80]. Furthermore, effective professional development supports teachers’ instructional development and, in turn, positively impacts students’ language performance [72]. However, other than the three studies conducted by the ELLA team, the rest of the studies did not provide sufficient information regarding the components of professional development for teachers. Additionally, though Saunders et al. [52] suggested the significance of professional development, no evidence was found in the paper on how to support teachers from over 30 schools across two states with efficient and timely training. Virtual professional development (VPD), which integrates situated learning and technology, was applied in studies with participants located across a wide geographic spread. For example, in the validation study of project ELLA, instead of traditional face-to-face professional development, Tong et al. [80] provided kindergarten teachers scattered across Texas with VPD and found that teachers shared open and positive attitudes towards virtually delivered training. This sheds light on future research that VPD could be an effective way to provide teachers with structured professional development.

According to Fisher and Frey [2], there are six major elements of oral language proficiency, and these elements are not strictly isolated from each other. However, the majority of the reviewed studies measured only two of them: acquisition of academic and domain specific vocabulary and/or phonological awareness of the sounds of a language. Kim [32] was the only researcher who additionally assessed ELs’ oral language proficiency with regards to syntactical knowledge and pragmatic knowledge with a self-designed instrument. The absence of the other elements might be due to the fact that current adopted standardized instruments on oral language proficiency are designed to measure a broad range of language proficiencies, including reading and writing, such as WLPB—R and WMLS—R. These instruments were not developed to measure different aspects of oral language development. Furthermore, compared to the measurement of morphological knowledge or discourse knowledge in oral language development, the assessment of phonological awareness and oral vocabulary awareness might be easier and more explicit for researchers and teachers to conduct without additional training. Future research should consider the development of an instrument that can be used to conduct holistic examinations of ELs’ oral language proficiency.

5. Conclusions and Limitation

One of the major components of the Sustainable Development Goals by the United Nations is to ensure quality education and lifelong learning for all [81]. It is critical to enhance and maintain students’ sustainability in language and academic learning. Although participants of effective intervention have increased oral language skills, those changes and improvement are only sustainable with continued teacher scaffolding and quality instruction. To support ELs’ sustainable language development, early intervention is necessary but not sufficient; continued and long-term instruction is needed as students progress to higher grade levels [19]. However, none of the reviewed studies followed up the intervention and examined what happened once the intervention was completed, particularly whether students’ oral proficiency was sustained, continued to grow, or decreased. The long-term impact of quality intervention is critical for schools and students, especially those with limited resources. Thus, future research should engage in follow-up studies that identify effective strategies that lead to the sustained development of students’ oral language performance, and in turn support their life-long academic learning.

Policies and practices to support ELs should be based on evidence-based research regarding how to improve academic performance. For English oral language development in kindergarten, the evidence summarized in this review supports a focus on effective intervention characteristics, including separate and extra English learning blocks, effective teacher–students interaction, and professional development for teachers. Results from this review can, in turn, shed light on the development of curriculum material and intervention programs to support ELs’ English oral language development. In addition, this study provides pedagogical implications and suggestions on the importance of the quality of intervention. Although ELs benefit from learning via L1, based on available resources and local situations, school districts and researchers should focus on improving the quality of intervention to better support ELs’ academic learning. More importantly, professional development in different forms (i.e., face to face or virtual) should be provided to support teacher’s instructional development and further enhance students’ academic learning. In addition, policies and school districts should broadly disseminate proven effective approaches to serve the academic needs of ELs.

It is important to note that the review methods applied in the current study have some limitations. First, the systematic review excludes qualitative studies and descriptive studies, as it required studies with pre- and post-outcome and comparison groups. Many such study exist and also provide intervention or practices that might be effective. However, these studies might fail to indicate how much students learned or improved through the intervention. Second, because the target population of the current review is kindergarten ELs, some studies that only include kindergarten students as part of their population but failed to report their academic performance at kindergarten were not included. Moreover, the current review was conducted within databases that are often applied in the fields of education and language learning. As a result, some other popular databases, including Scopus, were not included. Nevertheless, we further searched targeted journals, such as the Bilingual Research Journal and the Elementary School Journal, which are Scopus indexed. Finally, it is important to note that some of the studies reviewed took place years ago, and that political contexts and bilingual programs have changed. Therefore, it cannot be taken for granted that the interventions described in these studies can be replicated and applied to ELs today.