This paper focuses on two increasingly important issues in teacher education: the design of more skill-based education and the involvement of students by means of peer assessment. Ninety-three student teachers were trained in one important peer-assessment skill, namely 'defining performance criteria'. This training, which consisted of four peer-assessment tasks, was integrated in an existing course. Half of the group was trained in the skill of 'defining criteria' (experimental groups) and the other half was not (control group). By working on the peer-assessment tasks, student teachers in the experimental group learned to define performance criteria for a course content-related product. The effects of the training on students' ability to define criteria and the effects on the content-related skill were examined. Findings show that the student teachers from the experimental group scored significantly higher on the use of criteria, but did not surpass the control group on the content-related task performance.