While mathematics content courses are expected to provide future teachers with the needed content knowledge to become an effective educator, little is known about the effects of these courses on content knowledge development. In this paper, we report on the outcomes for 222 students from 13 Geometry for Teachers courses taken across the United States. We find that completing this course is positively associated with a growth in MKT-G scores similar to the growth in MKT-G scores that we would expect between the first and second year of experience teaching geometry. We also observe that these positive results are concentrated with course completers who are interested in pursuing a secondary mathematics teacher certification.