To diagnose classroom situations is crucial for teachers' everyday practice. The approach of worked examples with errors seems promising to support the diagnosis of classroom situations in student teachers (Stark et al. in "Learn Instr" 21(1):22-33, 2011). To enhance that approach, error-explanation prompts and an adaptable feedback method to help the learner realize why an error happened and how to prevent a recurrence might be beneficial. In this empirical study, we investigated whether error-explanation prompts and adaptable feedback can facilitate diagnostic competences. N = 108 student teachers took part in a 2 × 2 factorial design (with and without error-explanation prompts as well as with and without adaptable feedback). Error-explanation prompts had a positive effect on declarative-conceptual knowledge if combined with adaptable feedback. Student teachers might have realized a lack of basic concepts and focused their attention on the declarative-conceptual knowledge in the feedback. Contrary to our expectations, however, error-explanation prompts hindered rather than facilitated learning of practical diagnostic knowledge.