The purpose of this study was to determine the effect of an earth systems science course (integrated mathematics and science content) on preservice elementary teachers' mathematics and science teaching efficacy. Paired t-tests revealed that the personal mathematics and science teaching efficacy and science teaching outcome expectancy significantly increased over the course of the semester for the experimental group (those students enrolled in the earth systems science course). For the control group (those students not enrolled in the course), however, there was no significant increase. (Contains 3 tables.)