The aim of this study was to analyze the association among weight status based on body mass index (BMI) and the physical fitness level in Primary Education students. A sample of 71 students (boys, n = 36, girls, n = 35) volunteers aged 10-12 years participated in this study. The fitness tests were conducted during physical education classes (two sessions). In the first session was conducted body composition measures (weight, height and skinfolds-triceps and leg-medial-) and in the second session were administered tests of sit-and-reach, handgrip strength, standing long jump and Course Navette. They applied the Student t test for independent samples to analyze the differences between students with non-overweight and overweight / obesity. Non-overweight children had lower values of BMI, skinfolds, body fat percentage and higher values in the long jump, Course Navette, and maximum oxygen consumption than the overweight / obesity group. The lower performance in the Course Navette test and standing long jump test among children with overweight/ obesity might be explaind, apart from a real lack of fitness, by excess of fat mass. In contrast, overweight/ obesity children showed a tendency toward greater grip strength. These results could be explained because children with overweight / obesity also had a higher amount of fat-free mass. On the other hand, the flexibility measured by the sit-andreach appears not to be associated with BMI. Physical education teachers should choose those tests in which there was no influence of body mass during its execution.