This article reports a study of a university supervisor and a preservice English language arts teacher as they worked collaboratively within two different field experience sites to develop a conceptual understanding of instructional scaffolding. An analysis of classroom observations and mentoring conversations was conducted to examine how the supervisor supported the preservice teacher's transfer of tools for instruction from a university program to the high school classroom. Findings indicate the significant role of the teacher education program's conceptual base in fostering this transfer. (Contains 2 tables and 3 notes.)