This study analyzes gender differences in behavioral problems and school outcomes. The study is based on teacher and parent evaluations using the Strengths and Difficulties Questionnaire for approximately 6000 Danish children 10–12 years of age who were born in 1990–1992. The sample has been merged with extensive register data on parental background and student outcomes. Our findings show a large negative association between indicators of externalizing behavioral and school outcomes. Only a minor percentage of the gender difference in average reading and math test scores, however, can be attributed to gender differences in the prevalence of low-scoring individuals with behavioral problems.