1PRACTICING WHAT WE TEACH

Teacher education holds ironies that I suspect are absent in the education of other professionals. Because we are teachers of teachers, the principles we study, value, and carefully submit to our students as fundamentals of good practice have a way of doubling back on us. Consider, for example, the principle of good instruction which suggests that, when introducing students to new material, it is critical for teachers to link that new material with students ' existing knowledge of the subject (see Anderson, 1977; Rumelhart, 1980). This principle posits that some form of prior experience with the material is valuable—even essential—for learners who must come to understand a new novel, theorem, or historical attitude. The principle suggests that good teachers should, therefore, work hard to help students access relevant existing schema or build a prerequisite knowledge base. I am keenly aware—often uncomfortably aware—of the recursive nature inherent to my argument as I broach this principle with preservice teachers. Like a woman who stands between parallel mirrors and sees her reflection reflected back on itself in an infinity of progressively diminishing images, I ask myself whether I have acted according to the principle I am advocating. For even as we objectify and discuss the importance of the prior knowledge that high school students bring to the study of art, literature, math, science, and history, we cannot cease to function simultaneously a