While the methodology of formative intervention research has long been established, the aspect of new instrumentality of Change Laboratory is fragmentally documented. Therefore, in this study, we modified two major Change Laboratory mediating tools used in bilingual student-teaching seminars, namely the disturbance diary and four-field model. These two empirically investigated Change Laboratory tools have mediated transformative agency within the collective movement toward identity formation as the Change Laboratory participants (bilingual preservice teachers) conveyed their dilemma of to-be or not-to-be a bilingual teacher. We provide evidence on the relationship between the bilingual preservice teachers’ identity formation and their participation in the Change Laboratory intervention. The analysis made salient the role of two new Change Laboratory mediating tools, the adapted disturbance diary and individually generated four-field models, for the bilingual preservice teachers’ collective transformation in bilingual teaching. It also crystallized the importance of deepening the bilingual preservice teachers’ analysis of multiple languages and pedagogy as understood in the new bilingual teaching model in the Change Laboratory intervention.