Two charts side by side, twelve numbers in all, each with an empty tens column and an empty ones column to fill. The headers are colored, blue for tens and orange for ones, so the two places stay visually apart while a child works down the page.
This is the same idea as the underlined digit sheet turned around. There a child was asked to name a place; here they have to put a digit into one, which is a small step further and matches the chart most classrooms actually use on the board.
Ninety and forty are the two worth watching. A zero in the ones column looks wrong to a child who has learned that every box gets filled, and writing it anyway is the thing that has to be learned.
The numbers run from fifteen to ninety, so every one of them is two digits and none of them needs a hundreds column.