The study is aimed at determining the relationship between the index of physical activity and the motivation toward school tasks of Primary Education students. To this end, a descriptive, quasi-experimental design was employed. The instruments used for the study included PAQ-C and the Questionnaire on students' motivation toward their studies. Among the results, it should be noted that Primary Education students' motivation toward their studies is high, although the level of physical activity is relatively low for this age group. The level of physical activity is higher in boys than girls. The level of motivation, as well as achievement motivation, and causal attributions of achievement are higher in girls, but self-efficacy is higher in boys. The higher the level of physical activity practice, the higher the level of motivation toward their studies, but also the higher the achievement motivation, causal attribution and self-efficacy. Children with greater obesity levels have less motivation. According to these results, it is important to design actions that encourage the regular practice of physical activity, especially among girls. This should be done in different contexts, beyond the subject of Physical Education and in different populations. Interventions should take into account family and environmental factors, or the local environment and its resources.