With state and national policymakers eyeing ways to improve teacher preparation, a handful of education programs are becoming more intentional about how such "cooperating" teachers--as they're known in the lingo of teacher preparation--are selected and trained. That interest could grow as programs wrestle with the finer points of how to transform student-teaching from a haphazard, sometimes hastily tacked-on experience to the central component of preparation. The challenges seem to begin with the selection of cooperating teachers, a process that is often left to districts. There are other obstacles, too. For cooperating teachers, the rewards for taking on a teacher-candidate are generally paltry, and new teacher-related policies have added wrinkles: A nationwide push to make teacher evaluation more rigorous, sometimes using test scores as a factor, has made teachers hesitant to invite novices into their classrooms, educators say.