We found out that we needed to place the numbers so that even numbers were connected to odd numbers in order to have an odd difference. This meant we could mix the numbers up and find multiple ways of arranging the numbers in the grid.
EG:
5 4 7
6 9 2
1 8 3
We then tried the extension task of trying to arrange the numbers so that the difference between the connected numbers was always even. This was harder because we found that we either had to match even with even or odd with odd. We didn't have enough even or odd numbers to make the grid. We couldn't connect even and odd numbers as that would always leave an odd difference. We could find ways to complete this using our own numbers between 0-20 - either by using all odd numbers or all even numbers.