The Individually Prescribed Instruction (IPI) Project incorporates minute facilities for evaluating and improving its effectiveness constantly, where necessary, so that it may achieve its desired goals. A field test of IPI on 25 schools in the school year 1967-8 comprising three areas of inquiry emphasized this feature. The schools were tested and selected for how scrupulously they had applied the system and, this requirement satisfied, the methods of prescription setting were examined. This examination indicated where and how more variety could be achieved in the individual prescriptions for the children. An evaluation of the area of objectives revealed, not only redundancies, but also the fact that a test used for measuring an objective may itself need re-evaluation. Lastly, the effectiveness of lesson materials was tested and this showed that some materials were insufficient, and that the methods used for sampling some results were inadequate. Included is an appendix comprising materials and procedures used to obtain field data for the test. (GO)