Teachers can play a pivotal role in the early identification of children and adolescents with mental health problems. This study investigates how teachers perceive internalizing vs. externalizing problems among students. For this purpose, 345 sixth and tenth grade students in Germany completed the Strengths and Difficulties Questionnaire (SDQ). Additionally, their teachers were asked to nominate two students per class they believed were most likely to have emotional problems, and which two students per class they believed were most likely to have behavioral problems. The results show that teachers are able to identify children with mental health problems moderately. However, the correlation between teacher nomination and students’ self-report is considerably higher for externalizing symptoms than for internalizing symptoms. In addition, this correlation was higher for girls than for boys. Recommendations for teacher training and further research are presented.