We investigated whether the content pre-service teachers studied in elementary teacher preparation mathematics courses was related to their performance on a mathematics lesson planning task 2 and 3 years after graduation. The relevant mathematics knowledge was studied when the teachers were freshmen, 5 to 6 years earlier. Results showed that when there were differences in how completely graduates attended to the key mathematics concepts when planning lessons, the differences favored the topics studied in the courses, especially topics emphasized most heavily. We conjecture that teacher preparation can matter for lesson planning, an important task for teaching, if enough opportunities are provided to acquire the relevant content knowledge for teaching. We consider what this might mean for teacher preparation, more generally.