In this article Engelmann explains the importance of teaching to mastery and the necessity of having a curriculum program that does so. He describes the features of a Direct Instruction program, which teaches to mastery. The main features covered include properties of mastery, criteria and procedures for measuring mastery, procedures for teaching to mastery, procedures for aligning student skills with appropriate programs, and the benefits of learning to mastery. Engelmann concludes that teaching to mastery is the most effective use of instructional time and results in students learning how to learn. (Copyright © 2013, National Institute for Direct Instruction (NIFDI). All rights reserved).