There are many different conceptions of teacher effectiveness, and defining it is complex and sometimes generates controversy. Teacher effectiveness is often defined as the ability to produce gains in student achievement scores. This prevailing concept of teacher effectiveness is far too narrow, and this guide presents an expanded view of what constitutes teacher effectiveness. The guide outlines the methods available to measure teacher effectiveness and discusses the utility of these methods for addressing specific aspects of teaching. Those charged with the task of identifying measures of teacher effectiveness are encouraged to carefully consider which aspects are most important to their context--whether national, state, or local. In addition, the guide offers recommendations for improving teacher evaluation systems. The conclusion indicates that a well-conceived system should combine approaches to gain the most complete understanding of teaching and that administrators and teachers should work together to create a system that supports teachers as well as evaluates them. Appended are: (1) Validity and Measurement Terms; (2) Planning Guide; (3) Summary of Measures; and (4) Sample of Existing Evaluation Systems. (Contains 1 table.)