Little is known about how middle leaders address concerns with teaching performance. This study used a problem-based methodology and critical incident interviewing to elicit eight middle leaders' theories-in-use for 14 cases of concern. Our systematic analysis examined the beliefs constraining their actions, their actions as well as the resulting consequences. Our findings indicate common constraints across leaders including protecting relationships, accountabilities, their leadership approach and knowledge, and time. Concerns were rarely disclosed, subsequent actions were usually indirect, and little change in teaching practice resulted. The findings indicate the need for specific training and support for middle leaders in handling teacher-performance concerns.