How good are you at embracing learners’ mathematical mistakes? It’s time to break our habit of re-teaching for correctness and instead get curious about the space between right and wrong answers. John SanGiovanni reminds us that mistakes are not random, and when we take the time to “mine the gap,” we can dispel misunderstandings before they take root. Included are downloadable high-quality tasks, aligned to the standards of Grades K–2 mathematics.