The right types of technology can create new opportunities for students to demonstrate mathematical understandings and can strengthen existing formative assessment practices. The authors write that they frequently use the Math Learning Center apps--covering the range of manipulatives and models--to empower students to explain their thinking. The ability to capture, share, and discuss digital student work improves the feedback loop not only for the learner and the teacher but also for the whole class. The authors asked a group of second-grade intervention students who were struggling to "fluently add and subtract within 20 using mental strategies" (CCSSI 2010) to use the Number Rack app to showcase their approach to a problem. They report that the results were inspiring; each student engaged deeply with the technology and the authors were impressed by how much they could learn from the student work. Effective formative assessments do not require technology, but technology can offer meaningful advantages.