Three major educational revolutions have been the advent of writing, the use of books as teaching tools, and the shift in educational responsibility from the home to the school. The fourth revolution, which is based on the use of electronic technology in teaching, began with programmed teaching machines, individualized instruction, and the development of computer based education. This paper draws on meta-analyses conducted at the University of Michigan and the University of Colorado to review what has been learned from the application of educational evaluation and research synthesis tools to the area of instructional technology. Eight separate meta-analyses are covered, representing at least 500 separate studies. The results presented indicate that programmed instruction was more effective in recent studies than in earlier ones; individualized systems produce about the same results as conventional teaching at the elementary and secondary levels, although at the college level they are strikingly effective; and computer based education has real potential as a tool for improving student achievement. Eight references and four figures are appended. (LMM)