The Thinking Mathematics project, a joint effort of the American Federation of Teachers and the Learning Research and Development Center, had the primary objective of developing more efficient means of disseminating new knowledge about mathematics learning and instruction. The resulting practitioner-researcher collaboration developed an instructional approach based on current research findings interpreted by the clinical wisdom of classroom teachers. This approach, called Thinking Mathematics, formed the basis of an inservice training program implemented throughout the AFT's Educational Research & Dissemination network. Teacher change--and teacher conviction in the changes being advocated--was viewed to be critical for successful student learning outcomes. Pilot implementation of Thinking Mathematics occurred at five different sites across the country during the 1990-91 academic year, involving about 65 classes from grades K-5. Cognitive and affective effects upon students involved in the year-long implementation of Thinking Mathematics were assessed by using multiple sources of data: teacher self-reports of student change, standardized achievement test scores, student attitude survey findings, and problem solving test results. The teacher self-report data show that the teachers involved in the program perceived empowering changes in their students. Project students performed as well as or better than their non-project peers on both the Computational and Concepts and Applications subsections of standardized achievement tests. Student problem solving abilities improved, as measured by the Wood-Cobb problem solving tests. Positive student attitudes towards mathematics were revealed by the project's attitude survey: students' relatively lower motivation scale scores, however, suggest that they might not yet be ready to match their efforts with their generally positive regard for mathematics. Although the results reported should be considered preliminary, there are multiple indications that student learning and attitudes were enhanced by their participation in the Thinking Mathematics program. (Contains 43 references.) (Author)