Nature-oriented social-emotional learning in public preschools: a multi-site, three-arm randomized trial comparing outdoor learning with indoor delivery for preschool prosocial behavior in Slovakia and Spain

Abstract Outdoor learning is posited to potentiate social–emotional learning (SEL) in early childhood, yet cross-national randomized evidence remains scarce. We conducted a multi-site, parallel-group, three-arm randomized trial in public preschools in Slovakia and Spain to evaluate a 20-week, nature-oriented SEL curriculum delivered predominantly indoors (≤ 1 h outdoors weekly) or enacted through planned outdoor learning (≥ 4 h outdoors daily) against routine pedagogy (control; ≤ 1 h outdoors weekly). The study enrolled N = 272 participants: a child cohort ( n = 118; 54 boys, 64 girls) randomized within country to indoor-SEL, outdoor-SEL, or control, and adult cohorts of teachers ( n = 18; all female; 8 Slovak, 10 Spanish) and parents ( n = 136; 69 Slovak, 67 Spanish). The primary outcome was perceived prosocial behavior, independently rated by teachers and parents using the Questionnaire to Assess Perceived of Prosocial Behavior in Preschool Children (QSPBPCH) at pretest and posttest. Primary analyses used Group (indoor-SEL, outdoor-SEL, control) × Time (pretest, posttest) mixed-design ANOVAs with Bonferroni-adjusted contrasts; confirmatory linear mixed-effects models accounted for classroom clustering and country. Relative to control, both SEL arms showed greater pretest–posttest gains across rater groups; the contrast between outdoor- and indoor-delivered formats was not statistically significant at posttest. A nature-oriented SEL curriculum is feasible in public preschool systems and—whether enacted through outdoor learning or indoors—is associated with improved perceived prosocial behavior. Given the two-country scope and reliance on rater-reported outcomes, cross-cultural generalizability is interpreted cautiously; future research should incorporate independent observations, fidelity checks, and follow-up assessments.