Mastery learning is an instructional approach that relies on students successfully mastering material before moving on to the next lesson. It has been found to be a very powerful instructional method, with effect sizes ranging from 0.50 to 0.58, and is the fundamental component of many education interventions such as Response to Intervention (RtI), Personalized System of Instruction (PSI), and computer-based instruction. Mastery learning requires that instructional materials be sequenced so that instruction builds on what has been previously mastered until the overall learning objectives are mastered. Using formative assessment procedures, teachers frequently assess how each student is progressing toward mastering the objectives in each learning unit. Students who demonstrate competency move on to the next unit. Students may study in groups or alone, working through each unit, but progress is assessed individually. For students who have not mastered the lesson, additional group or individual instruction is provided. Remediation may include tutoring, peer monitoring, small group discussions, or additional homework. Mastery learning has been found to be effective at all levels of education.