The monograph describes various aspects of data collection, analysis and data-based decision-making for the regular or special education classroom teacher. Direct and repeated measurement of student progress and program effectiveness is advocated. Four fundamental steps are outlined: (1) identify instructional objectives and collect data on student performance; (2) display the data graphically; (3) examine the data and identify trends; and (4) use basic data decision rules to guide instructional decisions. The concept of "stages of learning" is introduced in relation to use of percent and rate data. Use of correct-to-error ratios and trials-at-criterion standards for setting performance goals is presented. Strategies for determining objectively when and how to change instruction are discussed. Instructional modification involves changing one or more of four basic program elements: general setting events, antecedent events, subsequent events, and the contingency arrangement. Finally, guidelines for implementing data-based instruction and making data-based decisions with students who are low achieving, exceptional and at-risk for dropping out are offered. (Author/DB)