The research design for this project is cross-sectional and longitudinal, and is designed to generate evidence that is descriptive (case study, observational, and design research) and associative/correlational (quasi-experimental). The project includes an intervention, which consists of using teaching experiment methodology (Steffe & Thompson, 2000) to follow the 16 case study students. This project collects original data using assessments of learning/achievement tests, and videography observation. To assess students' knowledge of measurement in Phases 1 and 3, the project will administer an extended version of the measurement and geometry subtest of the "Building blocks Asessment" (BBA), a measure of students mathematical knowledge and skills that features individual interviews of each student of about 20 minutes, with explicit protocol, coding, and scoring procedures. All BBA sessions are videotaped and the tapes and recording forms, including accuracy for each item and children's solution strategies and error types for relevant items, by trained coders. Any discrepancies are resolved via consultation with the senior researchers. All items are ordered by Rasch item difficulty; children stop the assessment after 6 consecutive errors.