Instead of actual textbooks, CPM classes use cheap paperbound workbooks that have absolutely nothing useful in them. While real textbooks include instructions, tables, equations, and examples that make it possible to learn by book alone, CPM books usually have none. CPM also places emphasis on (barely) supervised groupwork in the hopes that it helps students visualize mathematical concepts. Actually, all it does is destroy a student's ability to work on his/her own.
Teachers of such classes assume that CPM workbooks actually are textbooks and so don't really bother instructing students.