It has become necessary to monitor the change in learners' skills during the education carried out in electronic environments. In this study, pre-service teachers made a presentation in their teaching practice, and a formative assessment was given to ensure active participation of the observer pre-service teachers in the online peer assessment process. The observer pre-service teachers were asked to evaluate their peers' performances using a rubric. Based on the quantitative data collected and analyzed, questions about the experiences of the participants were created, and the opinions of the participants were obtained through e-mail. The research findings were obtained through the sequential explanatory mixed method. The study revealed that the observer preservice teachers could evaluate different performances consistently. The research also showed that the validity of the assessments was significantly low especially in the evaluation of low and medium level performances. The qualitative findings confirmed the quantitative findings.