Formative assessment is a continuum process of evaluating students’ performance to enhance students’ learning quality. The shift to full-online learning in pandemics reduces student-lecturer attachments during formative assessment. Therefore, we developed the Online Formative Assessment system (OFAs) based on a self-regulatory learning framework. Thisstudy aimed to explore the learning impact of OFAs, such as learning preparation, feedbackperception, and self-reflection. We used the mixed method with an exploratory approach. Wecollected quantitative data from 150 students who experienced OFAs, using 26 questionsadapted from AEQ (Assessment Experience Questionnaire) and analyzed by pre-post design(paired-T test). To explore a deeper understanding, we conducted 6 FGDs (N=28). Finally, weanalyzed the quantitative and qualitative data sequentially. We found the difference in students’preparation (p<0.5), feedback perception (p<0.5), and no difference in self-reflection (p>0.5).In Qualitative data, we found three themes as follows: (1) OFAs improve student preparationin learning; 2) Students are aware of being assessed during tutorials; 3) Require more specificand individual written feedback; 4) Lack of self-reflection due to unspecific feedback. Thesefindings represent that learning impact is a complex pathway that online assessment systems can drive. It needs externally driven feedback quality and internally driven factors such as self-reflection skills. However, we found the challenges to improving students' quality feedback and self-reflection skills. This study brings further research on student-lecturer engagement inonline formative assessment. DOI : 10.35990/amhs.v1n2.p71-78