Yale Public Schools (Yale, Michigan) conducted a field experiment in implementing mastery learning. The purpose of the experiment was to provide a hands-on experience for teachers in the implementation of mastery learning and to use students as their own controls in order to compare the results of the implementation of mastery learning both in terms of cognitive and affective student outcomes. Six classrooms were used in the sample for the experiment which included grades 3 through 6 plus a 5th/6th split grade and a special education resource room class, for a total of six teachers and 94 students. A series of six hour-long inservice classes were held to acquaint teachers with mastery learning. All six teachers chose mathematics as the content area for implementation. Test results compared the unit test scores in the fall of 1991 with the test results after implementation of two mastery learning units in the spring of 1992. Students were also assessed for any change in their feelings of self-efficacy using Brookover's Self-Concept of Ability Survey. Significant gains in achievement were found for both mastery learning units and self-efficacy. (Three tables and three figures of data are included; 20 references, verbatim reports of each of the six teachers on the implementation of the mastery learning units, the self-concept of ability scale, and the proposal for mastery learning experimentation are attached.) (Author/RS)