The Iowa Chautauqua Program was developed in 1983 with support from National Science Foundation (NSF) which awarded the National Science Teachers Association (NSTA) a major grant to study an inexpensive in-service model for stimulating reform in K-12 science classrooms. Iowa was one of the six Chautauqua sites which were modeled after a program for teachers from small colleges and operated by the American Association for the Advancement of Science. In Iowa this new Chautauqua effort focused upon Science-Technology-Society (STS) materials and teaching strategies with primary attention directed to teachers in grades 4 through 9. The program began with 30 teachers enrolled in a program in one center and increased annually to number 230 teacher enrolled in five centers across the state. The program was expanded with funds from various of private industries and Title II projects. Over 15,000 teachers have been enrolled during last two decades. The focus and unique feature was the STS teaching approach as reform in science education. This study investigates the effectiveness of the Iowa Chautauqua Professional Development Program. (Contains 7 tables and 1 figure.)