Biology and chemistry graduates (n = 29) on a one year, post graduate, initial teacher training course were asked about their perceptions of written lesson appraisals produced by mentors when observing their teaching. Data were collected using the same open questions at three points in their course. The data relating to mentors who had received only generic training were compared with those for mentors who had been trained to focus on topic-specific pedagogy. Marked differences in pre-service science teachers' perceptions are identified. The implications arising from these differences for using written lesson appraisals in developing topic-specific pedagogy are discussed and opportunities for future research identified. (Contains 4 tables and 1 figure.)