This mixed-method evaluation study examines relationships between the nature and characteristics of teachers' prior experiences and teachers' practice of standards-based instruction as a measure of instructional quality among alternatively certified mathematics and science teachers. The study found that career length, number of prior careers, and career relevance to subject area were not related to instructional quality. However, teachers with prior career experiences that were education-related practiced standards-based instruction to a greater degree than teachers with no education-relevant career experience. Implications of these findings for policy makers and practitioners are discussed. (Contains 3 tables.)