This paper examines, from the perspective of mediated action (Wertsch, 1991, 1998), the ways in which an experienced, primary-grade teacher used and continually modified an instructional too--"the practice page"--to mediate specific aspects of interactive writing, an approach to beginning writing instruction. The authors provide a detailed, theoretical account of the teacher's use of this instructional tool and argue that it provided a context for the kinds of explicit instruction and authentic activity that research demonstrates is essential to young children's literacy learning.