This report focuses on the long-range (i.e., two and one-half years later) effects of the National Science Foundation Summer Institutes of 1957 on the high school mathematics and science teachers who participated in them. Of the 4,600 high school teachers who had taken part in the Summer Institutes, 2,628 were involved in this study. Data were collected using questionnaires for principals, teachers who attended an institute, and non-attenders. The principals believed that developing enthusiasm for science among Institute participants was the main goal of the program. They believed the Summer Institutes fulfilled their purpose very well, and were more likely to call on an Institute alumnus rather than on any other teacher for advice on new teaching techniques. Among the benefits reported by Institute participants were: (1) they learned subject matter which was new to them; (2) they learned additional teaching techniques; (3) the Institute was a source of enthusiasm; (4) they extended social contacts; and (5) they were now teaching a new subject or more advanced sections. (BB)