Peer assessment is considered as a form of testing students' knowledge of online courses. The authors pay attention to the form of the problem statement and to the quality of the formulation of the evaluation criteria. The results of 947 responses to self-assessment assignments and 727 responses to peer assessment assignments are analyzed. A survey of students was also conducted. It is shown that the effectiveness of mutual verification depends on the correlation between the conditions of the formulation of the problem and the evaluation criteria. The authors recommend constructing the course so that peer assessment tasks are preceded by self-assessment tasks as training.