This study presents findings from the first cohort of teachers in a U.S. Department of Education Mathematics Science Partnership (MSP) grant designed to support the use of a standards-based elementary school mathematics curriculum, Investigations in Number, Data, and Space (Investigations). In line with the goals of the MSP program, the 84-hour professional development program focused on building teachers' knowledge of mathematics content, examining how the mathematics content is embedded into curriculum, and supporting teachers' enactment of reform-based pedagogies. Teacher participants had a positive gain in their content knowledge, but this increase did not have any statistically significant impact on student gains in the assessment of mathematics proficiency. Results about teacher beliefs were inconclusive, as more time is needed to change teacher beliefs. Teachers who changed their practices from teacher centered to student centered found their students with statistically more gains in their performance in curriculum-based mathematics assessments. Discussions and implications of these findings were also presented.