This five-part document presents three approaches to research on instructional improvement, with the final two sections concentrating on problems and implications for diagnostic prescriptive instruction. Part 1 reviews comparative instructional effectiveness studies. Part 2 discusses the Trait-Treatment Interaction Approach (TTI) which is concerned with the effects of instruction as they interact with individual differences. Part 3 focuses on the Systems Approach--comprehensive in its analysis of the learning situation. A model of this approach is presented in detail. Part 4 presents implications for research in diagnostic-prescriptive instruction. This section discusses research dilemmas and offers possibilities for coping with difficulties. It also includes a matrix of components and variables serving as a selective identification of research studies. Part 5 concentrates on implications of instructional improvement. This section offers a variety of diagnostic data and collection techniques and instruments which have been developed. (JS)