Everyone knows that arithmetic is true: 2 + 2 = 4. But surprisingly, we don’t know why it’s true. By stepping outside the box of our usual way of thinking about numbers, my colleagues and I have ...

A key part—though surely not the only part—of early-grades math is ensuring students get the basic arithmetic functions down and, beyond that, making sure they’re able to swiftly and automatically ...

Bundle the ones to make 10. Moving left on the number line. Skip counting. Gone are the days of rote memorization, constant addition and subtraction drills and learning long division before you knew ...