This submission has been collated from responses prepared by individual students in the Challenge Group. It replaces an earlier submission in which I had simply documented my observations of the group's work. I apologise for the duplication, I had not realised when I made the earlier submission that the problem would remain "live" for long enough for us to prepare our responses.
One student was puzzled by how one might tell if the pattern continued indefinitely. He knew it would work up to a 5x5 grid because he had checked, and he believed it would work for a 10x10 grid, and for a 100x100 grid, but was not sure about a 100,000x100,000 grid. He said that there would never be enough time to check for every number, and was perplexed by how to deal with this uncertainty. I thought instantly of the "Monstrous counterexample" article, I will have to try to modify it for a middle primary class!
With thanks,
Gina Meyers, Canberra, ACT, Australia
gina@ardenwood.com.au