The students then break into groups of two or three for 20 to 30 minutes, so that they can help one another on points they missed on the formative test. This process provides reinforcement for students who understand concepts and allows them to explain what they have learned to other students, often using an approach the teacher has not used or even considered. If the group gets stuck, they can call on the teacher, though Bloom notes they usually are able to work problems out on their own. Some students who need help beyond the group work are assigned supplementary activities that presents information in yet another form (workbook exercises, text readings, video tapes, etc...). According to Bloom, it usually takes these students no more than an hour or two to complete the work necessary to catch up. The class is then ready for an evaluative test, which is similar to but not identical to the formative test. In a pure mastery learning system, students who have not yet mastered the unit are recycled through the system until they do master it, with unlimited opportunities for working through the material until they can complete the evaluative test at a preset level of accuracy. In a modified mastery system, which will be discussed in the next section of this chapter, trials may be limited. In either case students either pass or do not pass the unit; their relative performance is not evaluated in comparison with other students' performance on the evaluative test. Not every student does master every unit, but studies have consistently shown that mastery students learn more than about 85 % of those taught in the traditional way. About 70 % of mastery students attain levels reached by only the top 20 % of students in traditional classrooms. Studies have also indicated that students who learn in mastery systems are better able to transfer material to other contexts, that mastery learning helps students learn how to learn through its presentation of material in a variety of formats, and that mastery approaches have substantial affective learning payoffs with students reporting greater interest in and more positive attitudes toward subjects taught through mastery. Bloom and his graduate students have also studied the use of the mastery approach in the preassessment phase of the instructional process. Students in second-year algebra and French classes who were given a preassessment test at the beginning of the year to determine what they recalled from the first-year course, and then re-taught the specific skills they lacked using the mastery learning corrective method, did far better on the first unit of the new course than did those in comparable classes that were offered only a general review of first-year concepts prior to beginning the first unit of the second-year class. When the prerequisite training was combined with a continuation of the mastery approach in the
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