This document reports on a small-group teaching experiment whose goal was to understand how fourth- and sixth-grade children develop concepts of common and decimal fractions. Both the Grade 6 and the Grade 4/5 children were taught common and decimal fractions through discussion and by using manipulatives, beginning with basic concepts of common fractions. Results showed: (1) common fractions were initially interpreted as parts of a whole, using region models; (2) Grade 6 students seemed to find manipulatives helpful, but Grade 4 students used manipulatives less and seemed more interested in completing as many questions as they could without recourse to manipulatives; (3) students were able to relate common and decimal fractions; (4) most students could develop fraction and decimal concepts, learn the associated operations meaningfully, and perform satisfactorily on end-of-unit tests; and (5) teachers felt they had learned much from their involvement in the project, including: the need for clarification of roles of researcher and teacher, importance of student interviews, usefulness of journals and student-constructed questions, and judicious use of worksheets. Appendices contain reports of lessons in Grade 4 and Grade 6, project evaluation by teachers and researchers, pre- and post-test questions, interview questions and transcripts, and worksheets. Contains 14 references. (MKR)