This review of research on instructional improvement and teacher evaluation considers the complex issues affecting the K-8 principal's ability to enhance educational quality through effective supervision of the instructional process. According to several studies, teachers found formal evaluations far less valuable than direct assistance and support. A recent study of improving school systems found that teacher evaluations focus on the formative process of observing teachers, arranging conferences with them, and recognizing them as professionals. Some studies found uniform procedures unsatisfactory because teachers vary widely in their abilities, experiences, styles, and needs. The studies suggest that principals need to take their own strengths and weaknesses as instructional leaders into account and obtain appropriate assistance in the instructional improvement effort. Experienced teachers can be a valuable source of such assistance because they understand the situations faced by other teachers and are trusted by them. The twofold role of the teacher supervisor--as a performance rater and as a guide to improvement--must be clear to both the supervisor and the teachers. Those who help teachers develop instructional improvement plans should be aware of the developmental phases identified in the research: diagnostic, tactical, and strategic. The process involves identifying and enhancing the "level of abstraction" at which each teacher operates. (PGD)