The big idea: unitizing

Place value rests on an idea called unitizing: treating a group of ten as a single unit you can count. This tool flashes structured base-ten arrangements — tens as rods of ten, ones as grouped dots — briefly, so students see the tens-and-ones structure of a number rather than counting every dot. The reveal builds the total by counting the tens back in (10, 20, 30…) and then bonds the number into its tens and ones, connecting the picture to the written numeral. Seeing quantities this way, and being able to name the same amount in more than one way, is what separates students who understand two-digit numbers from those who just recite digits. Keep the flash short and the discussion open: "How many tens did you see?" invites the structure to come out — exactly the understanding that regrouping later depends on.