The objective of the study was to verify the differences according to gender in the levels of physical activity, motivation, basic psychological needs satisfaction and responsibility in students of 5th and 6th grade of Primary Education (M = 10.51, SD = .53). In total, 68 students answered a series of questionnaires evaluating the intention to be physically active, motivation, the satisfaction of basic psychological needs, and the levels of personal and social responsibility. These subjects also wore an accelerometer for 1 week to objectively measure the level of Physical Activity (PA). There were 43 boys and 25 girls. Results show that boys had a higher index of PA during the week, especially at moderate intensity. Boys also had higher values of sedentary lifestyle. Significant differences were found in personal and social responsibility in favour of girls, finding no differences in the intention to be physically active. It is concluded that, girls had more adaptive values referred to responsibility. Furthermore, boys had a better adaptative values referred to PA lifestyle than girls but worse in sedentarism. It is highly recommended to objectively measure the PA levels to ensure reliable results to carry out the appropriate actions.