Background: Many students leave compulsory school without being qualified to apply for national upper secondary school programmes. Despite efforts, the number of unqualified students in Sweden has increased. Grades from compulsory school have direct implications for students' educational futures and the requirement to qualify for an upper secondary school programme is at least the grade G (pass), in the subjects Swedish/Swedish as a second language, Mathematics, and English. Earlier research shows that the amount of physical activity, students' motor skills, and grades in Physical Education can have an impact on school achievements, but no study has examined the relationships of these factors in this particular group of students. Purpose: The aim was to study relationships between physical activity and school performance among Swedish compulsory school students who fail to achieve sufficient grades to move on to upper secondary school (about one in five students in the city of Malmo). Method: The population consisted of 389 students of which 76% (147 male, and 146 female) participated in a web inquiry. For statistical analyses of the responses, the Statistical Package for the Social Sciences program was used. Non-parametric tests (Chi-squared, Kruskal- Wallis, and Mann-Whitney) were used to study differences between groups, and Spearman's rank correlation and Pearson's product moment correlation were used for correlation analyses. Findings: The results show that less than 50% were physically active in the school subject physical education and health (PEH), and 14% never participated. Forty-five per cent were never physically active during their spare time. Twenty-nine per cent failed to reach the goals in PEH. Nine per cent (14% of boys, and 4% of girls), received the highest grade in PEH: pass with special distinction. Significant correlations were found between the level of physical activity and grade in PEH, as well as between physical activity and total grades. Grades in PEH correlated with grades in Swedish, Mathematics, and English. Students who responded that they skipped lessons once a week or more, had significantly lower grades in PEH and in total than students who never or less often skipped school lessons. Students who had good self-esteem (n =162) were significantly more physically active than those who had low self-esteem (n = 32). Their answers to the question, "How physically active were you during school year nine?" showed that they moved and became breathless and sweaty more than students who had lower self-esteem. They also did sports/ exercise significantly more both in and outside of sports clubs. Conclusion: The findings of the relatively low levels of physical activity and the significant correlation between physical activity and school performance indicate the importance of examining how schools can improve students' self-esteem and motivation to be physically active and participate in PEH and other lessons.