This article discusses how math teachers at San Marcos High School turned to an online curriculum and in-class assessments to increase student achievement. Setting aside their 7-year-old textbooks, teachers filled the void largely with an online math curriculum, called Agile Mind, that comes equipped with an array of assessment tools. The idea was to get a better read on what their students know and what they should target in planning their classroom instruction. Agile Mind, a curriculum product in high school math and science, offers teachers multiple ways to use "formative assessment," a term generally used to describe classroom measures to give teachers and students feedback for adjusting instruction as it is taking place during the school year. Teachers use the items from the Agile Mind test bank to create mini-tests, quizzes, benchmark tests, or final assessments. The tests can all be administered online, then scored and analyzed, and compared against the scores of other students in the state.