Today's teachers and administrators are caught in a squeeze of conflicting demands. And evaluation guru Charlotte Danielson fears that teacher evaluation, as it's often implemented today, is making things worse. In schools where teacher evaluation has become simply a matter of numbers, ratings, and rankings, it may be undermining the very professionalism that's essential to positive learning environments for students. Danielson cautions that evaluation must include self-assessment, reflection on practice, and professional conversation. But even evaluation systems that include these components, she writes, should not be used as a school's main engine of teacher improvement. Instead, school principals should establish the school as a community of practice--a place of learning for adults as well as students--by (1) creating a safe, yet challenging environment, (2) establishing the expectation that colleagues will continually learn from one another, and (3) supporting teacher leadership.