While recognizing that instructional scaffolding in a whole-class context can engage students' learning as they move through individual zone of proximal developments (ZPDs), in this chapter, we argue that instructional scaffolding also can collectively engage a class through a shared ZPD when participant structures and discourse practices provide for co-participation and alter traditional notions of teacher support and shared responsibility. A case study of a chemistry classroom is presented to substantiate this argument and illustrate how instructional scaffolding can be used as a support for collective engagement. [This article originally appeared as NSSE Yearbook Vol. 113, No. 1.]