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 4,486 participating grade K, 1, and 2 students in 67 schools located in 10 public school districts in Florida during fall 2015. Focused on counting, word problems, and computation, the student assessment was designed to serve as a baseline measure of student achievement for use as a covariate in a randomized controlled trial evaluating the impact of a teacher professional development program called Cognitively Guided Instruction (CGI) on student learning.