One focus of a year-long study of West German apprenticeship was the conditions that are most supportive of learning on the job. The study design incorporated two distinctions that the Germans consider critical: manual versus white-collar occupations and size of training firm. Two occupations were studied--auto mechanic and "Industriekaufmann" (middle manager in an industrial firm). Twenty beginning and advanced apprentices were observed in large and small firms; and apprentices, their teachers, and workplace supervisors were interviewed. Four case studies were analyzed through use of a framework that consisted of four characteristics critical to assessing a workplace's potential as a learning environment: the mentor's role, the learner's role, the content to be learned, and the structure of learning. Four workplaces were analyzed as learning environments--a large auto repair shop, a small auto repair firm, a large industrial firm, and a medium-sized industrial firm. The case studies confirmed the value of attending to the mentor's role, the learner's role, content, and structure. Four needs for further research were identified: observation and interview data for tracking on-the-job teaching and learning; greater specificity, uniformity, and replicability in examinations of workplaces as learning environments; objective measures of what workers are learning; and exploration of how new workers process new experiences. (22 references) (YLB)