African American females are greatly underrepresented in STEM careers. Evidence suggests that one reason for this situation is that African American female students receive fewer opportunities to take advanced math and science courses in middle and high school. Theory suggests that implicit bias and/or negative stereotypes may lead counselors and school staff to track African American females into basic courses that have less academic rigor. Few analyses have sought to test whether professional development targeting negative stereotypes can produce increased enrollment in advanced math and science courses among African American students and change the behaviors/practices of school counselors regarding STEM advisement. The purpose of this study was to examine the effects of a professional development program for school counselors—STEM for All and All for STEM webinar in addition to a portion of the Engineer inclusion: Best Practices for Recruiting Students into Nontraditional STEM and CTE Programs and Pathways webinar—on the course enrollments of African American female students and STEM advocacy attitudes of school counselors. A pre-post single group survey study was performed in one district to test the effects of this professional development program. Twenty-two school counselors took the survey just before the intervention was given and 21 counselors took the survey post intervention. Wilcoxon signed-rank tests were run to determine the following: changes in overall school counselor survey pre/post scores, the intervention effect when controlling for several independent factors, and the intervention effect when controlling for single independent factors. Course enrollments for African American female students were collected and analyzed pre and post intervention. A Wilcoxon signed rank model for the proportion of Black females taking advanced math and science courses after the professional development intervention was conducted. Follow-up Wilcoxon signed rank tests were conducted by demographic characteristics including race and gender. Results revealed that there was no average improvement in school counselor STEM advocacy scores (representing advocacy beliefs and practices) or African American female STEM course enrollment as a result of the STEM intervention for school counselors. However, school counselors who identified as American Indian/Alaska Native as well as those who indicated that they work in both the middle and high school levels showed a significant improvement in STEM advocacy scores, respectively. In addition, school counselors who indicated they had 16 plus years of experience showed a marginal decline in STEM advocacy scores.