Ensuring that students have a strong foundation in mathematics by the end of 7th grade is essential if they are to move successfully into an advanced math curriculum that begins with algebra. But student achievement at the end of 7th grade varies widely in California--and this has consequences. Some 7th graders are taking a full Algebra I course; others are well positioned to take the course in 8th grade. But still others struggle with 7th grade content and could continue to do so for years. To improve students' chances to achieve in science, technology, engineering, and mathematics (STEM) fields in high school and beyond, schools must make sure that students succeed in math well before 7th grade. One measure of readiness is the California Standards Tests (CSTs) in mathematics, which students in grades 2-7 take at the end of each school year. This brief explores how across the early grades, more students are meeting the state's expectations; gaps in student performance that exist in 2nd grade persist; gaps in school readiness foreshadow later achievement gaps; early interventions could help close gaps in student performance; fragmented data provide an incomplete picture of readiness at the state level; and local educators and leaders are in the best position to examine students' progress in math. This brief is one of three on K-12 student achievement in mathematics for educators and policymakers wanting to strengthen science, technology, engineering, and mathematics (STEM) education in California. [This brief was prepared with input and advice from the California STEM Learning Network (CSLNet). For the other briefs in this series, see "California's Math Pipeline: The Grade 7 Pivot Point" (ED606336) and "California's Math Pipeline: Many Routes through and around College-Prep Courses. Issue Brief" (ED606366).]