"MyTeachingPartner--Math/Science" ("MTP-MS") is a system of two curricula (math and science) plus teacher supports designed to improve the quality of instructional interactions in pre-kindergarten classrooms and to scaffold children's development in mathematics and science. The program includes year-long curricula in these domains, and a teacher support system (web-based supports and in-person workshops) designed to foster high-quality curricular implementation. This study examined the impacts of the intervention on the development of mathematics and science skills of 444 children during pre-kindergarten, via school-level random assignment to two intervention conditions ("Basic: MTP-M/S" mathematics and science curricula, and "Plus: MTP-M/S" mathematics and science curricula plus related teacher support system) and a Business-as-Usual control condition ("BaU"). There were intervention effects for children's knowledge and skills in geometry and measurement as well as number sense and place value: Children in "Plus" classrooms made greater gains in geometry and measurement, compared with those in "BaU" classrooms. Children in "Plus" classrooms also performed better on the number sense and place value assessment than did those in "Basic" or "BaU" classrooms. We describe the implications of these results for supporting the development of children's knowledge and skills in early childhood and for developing and providing teachers with professional development to support these outcomes.