This longitudinal mixed-methods study investigates the efficacy and sustainability of instructional coaching outcomes among urban elementary teachers (N = 36) using focus group and quantitative pre-, post-, and 1 year-after intervention data. Coached teachers participated in a 30-hr workshop and then seven cycles of coaching (15 hr) targeting use of five research-based principles of learning—the Standards for Effective Pedagogy—for teaching diverse students. Findings demonstrate instructional coaching led to statistically significant (a) pedagogical transformation and (b) patterns of sustainability and attrition. Implications for theory, practice, and research are derived by interpreting quantitative and qualitative findings together.