For several years I have been delivering a student-centred portfolio-based module intended to encourage and develop critical reading skills in final year life sciences students. The module uses the scientific literature around biological research into schizophrenia as a vehicle. Students are expected to read a number of research papers in various aspects of this work, providing a critical appraisal of each. Portfolios are assessed periodically so that they get feedback as the module runs. This project has exploited a stack of archived coureswork portfolios to examine if there is evidence that progressive development of critical reading skills occurs through the course of the module; that is, is the module effective in delivering its aims? The method has been to re-examine the students' comments on papers in a number of portfolios submitted earlier and later in the module, assessing whether they are evaluative.