This report provides a description of the development process, field testing, and psychometric properties of a student mathematics test designed to assess grades K, 1, and 2 student abilities. The test was administered to 4,535 participating grade K, 1, and 2 students in 66 schools located in 9 public school districts in Florida during spring 2016. Focused on number, operations, and equality, the student assessment was designed to serve as a baseline measure of student achievement in a randomized controlled trial evaluating the impact of a teacher professional development program called Cognitively Guided Instruction (CGI) on student learning.