The Yale Summer High School (YSHS) is an experimental program addressed to the development of high-potential, underachieving students from disadvantaged backgrounds. To evaluate the long-term effectiveness of the intervention, an experimental design including random selection of samples, two control groups (one matched for a test of generalization, and the other not so matched), and two year follow-up procedures were instituted. The initial testing of all groups included personality, intellectual, and background factors. Thefollow-up involved school performance, college attendance, and other plans. The major results were as follows: the matched control group demonstrated similar career patterns to the YSHS; and the non-matched group attended college less often, going on to technical school, work, and military service. The experimental design and long term evaluation is considered to lead to the following conclusions: (1) there were no appreciable differences between the experimental and matched control groups; (2) utilization of only the non-matched though highly selected group would have led to an over-estimation of the effectiveness of the YSHS program; and, (3) since equally outstanding students did as well as those who attended, such programs might better address themselves to the students who have been ignored by the local public schools and who might be the greatest beneficiaries of innovative educational endeavors. (Authors/RJ)