Formative assessments are an instructional tool used to gauge student learning. Moreover, formative assessments provide a practical way to differentiate instruction to diverse gifted students. In a federally funded research study conducted in 11 states with 87 teachers and 1,179 gifted third graders, observational and interview data was collected and analyzed to determine the effectiveness of formative assessments, as well as teachers’ perceptions of this strategy. This mixed-methods study employed Erickson’s Analytic Induction and ANCOVA analysis to determine the effect of teacher use of formative assessment data with fidelity upon learner post-test performance outcome.