This paper presents the evolution of and the lessons learned from a research approach to assessment of student outcomes, specifically of student academic achievement, being used by the Puerto Rico Statewide Systemic Initiative (PR-SSI), which is one of the statewide systemic initiatives for science and mathematics sponsored by the National Science Foundation. A participatory-research approach was selected for the evaluation and assessment of the PR-SSI in general and for the assessment of student academic achievement in particular. Triangulation of results has been a major element of the design from the beginning of the reform. Two different versions of the PR-SSI's model were developed. The evolution of the first and second versions show that considerable organizational learning took place within the PR-SSI. The final model, which incorporates information from the Third International Mathematics and Science Study and the engagement of teachers and administrators, challenges traditional notions of participant involvement in evaluation because it requires direct contributions to use results to improve teaching and learning and the teamwork of evaluators and content specialists to lead the self-assessment process. (SLD)