The discussion on the dynamic assessment (DA) -- a combination of assessment and instruction -- and regulatory scales from implicit to explicit corrective feedback (CF) is relatively new in the CALL context. Applying the notions of Sociocultural Theory, Zone of Proximal Development (ZPD) and Mediation, the present study examines how a DA-based regulatory scale from implicit to explicit CF could be designed to promote language learning in the text chat environment. This was done in collaboration with teachers. Four English-as-a-second-language (ESL) teachers and eight ESL students participated in the study. Using the methodology of design-based research (DBR), the study was conducted mainly in three stages: exploratory stage, first intervention, and second intervention. This study drew on various data. Naturally occurring interaction data such as teachers' oral conversation transcripts and text chat transcripts were analysed using conversation analysis, while the teachers' interviews were analysed using thematic analysis. Thus, employing DBR, the present study introduces a three-step regulatory scale that could promote learning in the text chat environment. The findings suggest that the three-step regulatory scale could be used by teachers to identify the learner's potential and assist them in partial or complete self-regulation. The study will introduce a DA-based regulatory scale to promote language learning in the text chat environment and contribute to the knowledge of DA, ZPD and mediation in the CALL context.