Despite the theoretical argument and empirical evidence regarding the impact of self- assessment on academic achievement and self-regulated learning (SRL), the mechanism for this impact is understudied. The present study aimed to investigate the characteristics of self-assessment practices at different SRL phases and its relationship with academic achievement. Using a course assignment as the learning task, sixty-three students enrolled in a one-year master programme in a teacher education institute responded to an instrument assessing their self-assessment practices (including four self-assessment actions) at the SRL Preparatory, Performance and Appraisal phases of the task. Their final scores of the assignment were also collected. The results showed that self-assessment is a fundamental skill for SRL and occurs at each SRL phase with different patterns. Autoregressive relationships were found for all self-assessment actions between different SRL phases. Self-reflection at Performance phase was found to influence feedback seeking at Appraisal phase. Self-directed feedback seeking through monitoring at Performance phase was the strongest and positive predictor of academic achievement; and achievement had negative impact on all self-assessment actions at Appraisal phase. This study may assist educators and researchers to better understand the complexity of self-assessment in relation to learning process.