Effective schools are typically defined as those schools which improve or maintain already-established high levels of student achievement. A number of issues and research needs are raised which relate to the identification of effective schools. Unless the nature of "effectiveness" can be described and agreed upon, researchers face the possibility of identifying variables related to the concept not accepted by those responsible for teaching children. Research, program improvement, school district-wide planning or funding decisions, and rating or ranking schools are all potential purposes for identifying school effectiveness. There is a need for a variety of different measures, for separating school effects from other influences, for selection of an appropriate achievement measure, for means by which scores or other indicators can be aggregated, for defining success related to objectives, and for consistency. The identification of "transition" schools (those emphasizing improved ratings, yet with low achievement scores) and "false negative" schools (with uniformly low ratings on success factors, yet high test scores) is considered. The effects of funding on schools, and the need for data linked to effectiveness indicators are examined. The critical issue suggested is the extent to which a school maximizes its effort to improve each student's potential. (CM)