Three Digit Column Add Tower

About Three Digit Column Add Tower

Three Digit Column Add Tower takes the written method a child learned with two digits and shows that nothing new is required to make it three. That is the genuine lesson of this stage and it is easy to miss: children who have been drilled on two-digit sums often treat a three-digit one as an unfamiliar problem, when in fact the same procedure simply runs one column further to the left. Making the layout identical to our two-digit game is deliberate for exactly that reason — the grid looks the same, the carry row behaves the same, and only the width has changed. What is new is that a carry can now land in the hundreds as well as the tens, and sometimes both in the same sum, which is where children who have been carrying by habit rather than by understanding come unstuck. The carry row shows each carried ten above the column it lands in, never above the ones, because nothing is ever carried into the ones and a child copying the layout should not learn otherwise. The first two levels display the carries so the child completes only the answer and can see where each one came from; from the third level the carries are theirs to work out. Every empty cell has a clue naming the column being added, with a fuller hint behind a button. Grids are worked by tap or keyboard, every cell announces its position to screen readers, and a wrong digit flashes and can be replaced. Free, no sign-up, no advertising to children.