Large classroom population in Korean schools has necessitated the development of an educational model which (1) is effective with a large heterogeneous group of students; (2) does not require an overload on classroom teachers; (3) does not presuppose massive teacher retraining; and (4) is adaptable to a wide range of existing school situations. An instructional model, the Mastery Learning Project, was devised with the following components: (1) diagnosis of learning deficiencies; (2) compensatory programs; (3) presentation of learning objectives; (4) teacher instruction with emphasis on charts and audiovisual materials; (5) formative tests; (6) remedial programs for those failing in mastery; (7) enrichment programs for those attaining mastery; (8) cooperative learning activities; and (9) summative tests. Two studies involving respectively 272 seventh-grade students (half control, half experimental) showed a high rate of success for the experimental groups. Evaluation techniques were employed at a number of points in the educational process: a diagnostic test at the beginning of the unit, formative tests at the midpoint, summative tests upon unit completion, and tests for "serendipity effects" (such as problem solving ability, creativity, critical thinking, and other outcomes not specified as learning objectives). The project has now been extended to 630 schools at the seventh-eighth-and ninth-grade levels. (An evaluation of the project by the Director, Department of Planning and Financing of Education, UNESCO, is appended.) (MB)