School-Based Intervention to Improve Nutrition Knowledge and Lifestyle Awareness Among Adolescents: Results from an Italian Quasi-Experimental Study

Background/Objectives: Adolescence is a critical period for the adoption of health-risk behaviors and the development of non-communicable diseases (NCDs). Schools represent a strategic setting for health promotion interventions; however, Italian studies simultaneously assessing NCD-prevention knowledge and lifestyle behaviors in the same adolescent population remain scarce. The study aimed to evaluate improvements in knowledge regarding nutrition and other lifestyle-related behaviors among Italian adolescents following a school-based educational intervention. Secondary objectives included describing lifestyle behaviors within the study population and exploring participants’ evaluation of the intervention. Methods: A quasi-experimental pre-post study was conducted between March and May 2025 in five lower secondary schools. A total of 410 adolescents aged 11–16 years were enrolled through a two-stage cluster sampling procedure. The intervention, lasting approximately two hours, was delivered by a trained nurse-researcher and addressed four health domains: nutrition, physical activity, screen exposure, and substance use. Results: Following the intervention, a measurable increase in overall knowledge scores (mean increase: +3.9 points) was observed, with 88.9% of participants showing improvement. The largest improvements were observed in nutrition-related knowledge and awareness of passive smoking harms. Despite these gains, unhealthy behaviors remained prevalent, including low adherence to physical activity recommendations (36.1%), suboptimal dietary quality (39.9%), and high screen exposure. A linear regression model identified five independent determinants of higher knowledge improvement: older age, female gender, higher screen exposure, having at least one employed parent, and lower pre-intervention test scores. The intervention was positively evaluated, with high levels of satisfaction, clarity, and perceived usefulness. Conclusions: Nevertheless, the persistent gap between knowledge and behavior underscores the need to integrate motivational and environmental components, gender-sensitive approaches, and longitudinal evaluations to foster sustainable, healthy choices and contribute to NCD prevention.