Physical Literacy-Focused Education Improves Fitness Markers in Preadolescents: Implications for School-Based Health Promotion

Background/Objectives: Physical literacy (PL) is globally recognized as a foundational determinant of health status in children, but the effects of interventions based on PL were rarely studied in preadolescent children. The aim of this quasi-experimental, school-based study was to evaluate the potential effects of a PL intervention delivered during regular school hours on physical fitness (PF), physical literacy (PL), and physical activity (PA) in children aged 9 to 11 years from southern Croatia. Methods: Participants were 125 preadolescents (57 girls), and were grouped into a control group (C = 70), and an experimental group (E, n = 55). The E group participated in a specific PL-focused education, integrated into regular physical education (PE) lessons as a 5–6 min substitute for standard PE content, over 12 weeks (36 PE classes in total). The C group participated in the standard PE curriculum. A pre–post–retention design was used, and the observed variables included anthropometrics (height, weight, BMI), PF (jumping power, abdominal strength, upper body strength, flexibility, mobility, and cardiovascular endurance), PL (evaluated by the PLAYself questionnaire), and indirectly measured PA (estimated via the PAQ-C questionnaire). Multivariate (MANOVA and univariate (ANOVA) analyses of variance for repeated measurements were used with time, gender, and group as the main effects, including their interactions. Results: MANOVA calculated for a set of PF variables revealed significant main effects for time (F = 1361, p < 0.001) and a significant time × group interaction (F = 2.98, p < 0.05). Univariate ANOVA indicated specific intervention effects for jumping power and abdominal strength, favoring the E group. No significant differential effects were observed for PL or PA. Conclusions: The study demonstrated small, but statistically significant, improvements in PF indicators among children exposed to the PL-based intervention. Notably, the intervention was conducted in authentic school settings using standard resources, supporting the ecological validity and real-world applicability of the findings.