This activity can give pupils the opportunity to extend their understanding of squares. It may help pupils who have got used to calling tilted squares "diamond shapes". When using a larger grid they can see a variety of "tilts" that a square can have on such a grid.
It would be good to have some practical experiences like using pegboards, or perhaps the playground with dots marked in a similar way and the children deciding where 4 pupils could stand to make a square, etc. while listening to each other's statements about what makes a square. When you then give them access to the interactive game it is helpful to ask them to work in two's and encourage discussion about good and bad moves.
How have you decided where to put your mark?
Are there some ways of always winning?
What is the change when playing with more dots on the screen?
If the pupil does not seem ready to approach this interactive game then it may be worthwhile looking at Complete the Square first.