The purpose of this study was to determine change in environmental education teaching efficacy beliefs of K-12 teachers who participated in two weeks of an intensive summer earth systems science institute using the Global Learning and Observations to Benefit the Environment (GLOBE) curriculum as the conceptual framework. Thirty-eight teachers participated daily in eight hours of Basic GLOBE activities the first week and Advanced GLOBE activities the second week. In addition, teachers participated in one orientation session, two follow-up seminars, and were required to develop an action implementation plan to implement GLOBE activities and protocols into their classrooms during the following fall semester. Teachers were given the Environmental Education Efficacy Belief Instrument (EEEBI) at the orientation session, on the last day of the summer activities, and a third time at the last follow-up seminar in the fall. These scores were analyzed for any significant change in "personal environmental teaching efficacy" (PETE) and "environmental teaching outcome expectancy" (ETOE). Results indicated that teachers reported significant gains in both PETE and ETOE immediately following the workshop. While mean scores on the two subscales increased slightly between the conclusion of the summer institute and the end of the fall semester, the increase was not significant. (Contains 3 tables.)