Alternative certification programs provide a potential solution for teacher shortages in high-needs settings and content areas. These programs often attract career changers, who bring a passion for their content area and a desire to make it relevant to students. Research suggests that support during the first year is critical, but little is known about why some career changers do not complete their program or complete but do not teach. In this study, we explored program and teacher attrition using a variety of factors collected from 58 participants across six cohorts of an alternative certification program focused on mathematics and science teaching in urban middle schools. In addition, we analyzed qualitative data from eight case studies. While race was related to program completion, personal factors drove participants' choices to enter and stay in teaching, such as marital status, number of children, advanced degree, and age. Implications for supporting career changers are discussed.