Low teacher self-efficacy is an important factor constraining the teaching of science at the elementary level. This study was designed to investigate the effectiveness of particular sources of efficacy information for enhancing the science teaching self-efficacy of practicing elementary teachers. Twelve teachers participated in an intervention that was designed to provide them with cognitive mastery, enactive mastery, modeling, and verbal persuasion. Data were collected prior to, during, immediately after, and 2 years after the intervention. The results showed that increases in self-efficacy were mainly due to cognitive mastery (i.e., perceived success in understanding how to teach science) and in situ feedback (i.e., verbal persuasion given after observation of the teacher teaching his/her own class). (Contains 1 table.)