Here we have one page from a selection found in Year 2 which looks in detail at a 1-100 number square and is excellent practice at understanding place value as well as counting. We often take it for granted that children can count up to 100 easily, but in fact many children are not at all confident with this.
A small section of the whole number square, just 4 by 3 is taken and most of the numbers removed. The skill is in replacing the missing numbers correctly.
This can be done in a variety of ways. Probably the easiest way is to work across as each number is one more than the number to the left. One of the more interesting ways is to work down as each number is 10 more than the number above.