Reasoning about the number of matches needed to build squares that
share their sides.
We can arrange dots in a similar way to the 5 on a dice and they
usually sit quite well into a rectangular shape. How many
altogether in this 3 by 5? What happens for other sizes?
Compare the numbers of particular tiles in one or all of these
three designs, inspired by the floor tiles of a church in
Suggest using a standard $10 \times 10$ 'table-square' to help with the tables. If even this is proving difficult, start by using a $10 \times 10$ 'table-square' [such as this one] that can be written on and crossing out the tens figures. The resulting
unit-numbers can then be transferred to a plain sheet of squared paper. This ready-made sheet might help.