210 children (110 girls and 100 boys) were interviewed individually about causes that lead to success or to failure in school tests. They were presented fictitious scenarios about an unknown peer who had either success or failure in a dictation task and a sums task. The free answers were taken as mirroring means-ends beliefs of the interviewed persons. A content analysis of the answers led to the differentiation of 30 different categories. Practice, specific abilities, and concentration were mentioned most frequently both in success and in failure situations. The gender differences were more pronounced in failure than in success situations: For boys, it was rather the (lack of) instant effort that counted, whereas girls stressed more the (lack of) lasting effort, e.g., preceding practice. As compared to children, adolescents mentioned more often specific abilities, fast understanding, practice, and didactical presentation, and less often extrinsic motivation. A cluster analysis and a principal components analysis proved that the 30 basic categories overlap partially and can be combined into eight groups of categories. (Contains 2 tables, 3 figures and 3 notes.)