To enhance the effectiveness of formative assessment and self-regulated learning, this study focused on evaluative judgement. A process for developing evaluative judgement and co-regulation had proposed. However, this co-regulation and evaluative judgement model lacks validation for use in classroom settings; the process of developing evaluative judgement remains unclear. Thus, this study aims to examine the processes of co-regulation and development of evaluative judgement by applying the co-regulation and evaluative judgement model in a Japanese elementary school. We confirmed that evaluative judgements are shared with students through co-regulation and that both evaluative judgements and learning outcomes are enhanced. The results support the co-regulation and evaluative judgement model and partially reveal the process of the development of evaluative judgement. Evaluative judgements are expected to expand the effectiveness of formative assessment and self-regulation.