Delivery and Receipt of a Self-determination Theory-based Extra-curricular Physical Activity Intervention: Exploring Theoretical Fidelity in Action 3:30.

The implementation, fidelity, and receipt of a self-determination-theory-based after-school physical activity intervention (Action 3:30) delivered by teaching assistants (TAs) was examined using a mixed-methods process evaluation. Physical activity motivation and need satisfaction were reported by 539 participants at baseline, the end of intervention, and 4-month follow-up. Pupil- and TA-reported autonomy-support and teaching efficacy were collected alongside interviews with 18 TAs and focus groups with 60 participants. Among intervention boys there were small increases in identified, introjected, and external motivation and no differences in need satisfaction. Among girls, intrinsic and identified motivation and autonomy and relatedness were lower in the intervention group. Qualitative evidence for fidelity was moderate, and boys reported greater need satisfaction than girls. TAs provided greater structure than involvement or autonomy-support and felt least efficacious when facing school-based challenges. The findings highlight the refinements needed to enhance theoretical fidelity and intervention effectiveness for boys and girls.