Purpose: This study set out to investigate pupils' evaluations of their academic abilities in different school subjects and their ratings of their potential for improving their performance in those school subjects. Sample: Twenty-eight pupils from the third grade (approximately age nine) and 30 pupils from the sixth grade (approximately age 12) in a primary school in Finland were interviewed. Design and method: The interview included tasks where the pupils were asked to rate and explain their potential for improvement in mathematics, the foreign language and the mother tongue. The explanations given were content-analysed and coding categories were formulated on that basis. Results: In all the three school subjects, the third-graders had a more positive view of their ability and its potential for improvement than the sixth-graders, and they based their view on a perspective of development and learning new things. The sixth-graders were more moderate and more uncertain in assessing their future performance. Conclusions: This study provided support to the earlier findings to the effect that pupils' faith in their abilities decreases in the course of their school years. We seek to explain this phenomenon in terms of the early stabilisation of the pupils' school performance, which is conveyed and constructed in the school's evaluative practices, especially in normative assessment. These practices clearly convey a differential conception of ability, which the pupils adopt as part of their self-assessments as shown e.g. by their use of school-like explanations in assessing their performance. (Contains 2 figures.)