Teachers working with students with reading difficulties must decide when and how to intervene. Wood (2002) suggested that teachers' shift their levels of support to match students' needs based on moment-by-moment observations--that is, teachers should scaffold their support. In this qualitative analysis, we investigated instructors' scaffolding of strategy use during tutoring lessons with sixth-grade struggling readers. As students thought aloud about astronomy passages, teachers made contingent instructional decisions. Lesson transcripts were coded for Wood's levels of contingent intervention (i.e., general verbal, specific verbal, specific verbal with nonverbal, preparation for action, and demonstration) and repair processes. Instructors constructed some successful scaffolds but more often demonstrated or interrupted readers' problem solving with "preemptive prompts." Implications for instruction and teacher preparation are discussed. (Contains 3 tables and 2 figures.)