The Ongoing Assessment Project (OGAP) is a learning trajectory-oriented formative assessment program that develops teachers’ abilities to understand and apply research-based developmental trajectories in math content areas to deepen their thinking about their students. In OGAP, teachers learn to use a learning progression framework to continually assess and adapt their instruction to students’ developing understanding, aiming to move them towards more sophisticated strategies in a range of multiplicative contexts. For this reason, OGAP puts a premium on students’ precision of answer (including correctness and unit labeling) and sophistication of solution response. In this study we examine the multi-year impacts of OGAP on grades 3-5 student correctness and solution sophistication in multiplication on an open-ended assessment created by the Consortium for Policy Research in Education (CPRE) as part of a randomized experimental study of OGAP in Philadelphia schools. In order to assess the intervention’s impact on student learning in both correctness and sophistication, the research team developed an assessment measure with three vertically-equated grade-specific forms composed of open-ended items. The assessment asked students to show their work to allow for analysis of their correctness, strategies, and errors. The results show strong and consistent first year effects on student correctness and solution sophistication multiplication outcomes in all three grades that were assessed. However, these results did not persist during the second year of OGAP treatment, which focused on fraction, when controlling for end of first year results. When examining the second-year multiplication results using the baseline measure, the treatment impacts were present, reinforcing the strength of the first year effects. The next step is to examine year 2 effects in fractions, which was the focus of the second year of OGAP professional development. Additionally, since student and teacher turnover are manifest in Philadelphia, and consequently both students and teachers had different levels of exposure to OGAP, additional analyses are needed to incorporate student and teacher levels of exposure and implementation of OGAP into the models, to disentangle results by level of treatment.