This study tested a model of motivation based on self-determination theory (SDT) in the context of school physical education (PE). The primary aim was to examine the impact of a need-supportive environment on students' motivation and related outcomes. The study also explored the invariance of the model across gender. **Methods:** - **Participants:** 950 British secondary school students (443 males, 490 females, 17 gender not specified). - ** Measures:** Need support (autonomy, competence, relatedness), need satisfaction, motivation (intrinsic, extrinsic, amotivation), concentration, positive and negative affect, and preference for challenging tasks. - **Data Analysis:** Structural equation modeling (SEM) and multisample SEM invariance analysis were used to test the model. **Results:** - **SEM:** The model fit the data adequately, with need support positively predicting need satisfaction, which in turn predicted intrinsic motivation and adaptive outcomes. Need satisfaction negatively predicted amotivation, which was positively predictive of unhappiness. - **Multisample SEM Invariance:** The model was largely invariant across gender, with some minor differences in the paths between need satisfaction and introjected regulation. **Discussion:** - **Importance of Teacher-Created Environment:** The study highlights the importance of creating a need-supportive environment to promote self-determined motivation and adaptive outcomes. - **Invariance Across Gender:** The model was largely invariant across gender, with some differences in the paths between need satisfaction and introjected regulation. - **Future Directions:** Future research should examine multiple social agents and objective measures of need satisfaction, and explore longitudinal patterns of motivation and its consequences. The findings support the application of SDT in PE and suggest that physical educators should focus on fostering a need-supportive environment to promote intrinsic motivation and positive engagement in students.This study tested a model of motivation based on self-determination theory (SDT) in the context of school physical education (PE). The primary aim was to examine the impact of a need-supportive environment on students' motivation and related outcomes. The study also explored the invariance of the model across gender. **Methods:** - **Participants:** 950 British secondary school students (443 males, 490 females, 17 gender not specified). - ** Measures:** Need support (autonomy, competence, relatedness), need satisfaction, motivation (intrinsic, extrinsic, amotivation), concentration, positive and negative affect, and preference for challenging tasks. - **Data Analysis:** Structural equation modeling (SEM) and multisample SEM invariance analysis were used to test the model. **Results:** - **SEM:** The model fit the data adequately, with need support positively predicting need satisfaction, which in turn predicted intrinsic motivation and adaptive outcomes. Need satisfaction negatively predicted amotivation, which was positively predictive of unhappiness. - **Multisample SEM Invariance:** The model was largely invariant across gender, with some minor differences in the paths between need satisfaction and introjected regulation. **Discussion:** - **Importance of Teacher-Created Environment:** The study highlights the importance of creating a need-supportive environment to promote self-determined motivation and adaptive outcomes. - **Invariance Across Gender:** The model was largely invariant across gender, with some differences in the paths between need satisfaction and introjected regulation. - **Future Directions:** Future research should examine multiple social agents and objective measures of need satisfaction, and explore longitudinal patterns of motivation and its consequences. The findings support the application of SDT in PE and suggest that physical educators should focus on fostering a need-supportive environment to promote intrinsic motivation and positive engagement in students.