This is a note from Pippy’s dad, again, in praise of Chris and the team at OpenMind for Numberjacks.
Some years ago (from 1989-1992), I had the good fortune to be accepted to Balliol College, Oxford, to do a degree in Mathematics and Computation.
Dr. Frances Kirwan (who later became president of the London Mathematical Society) was one of my tutors. While I was an undergraduate, Frances had one of her children, who is now at Cambridge (reading Mathematics.)
Anyway, I recently went to a mathematicians reunion dinner at Balliol, and met up with Frances again, and inevitably the subject of mathematical literacy in children came up. I mentioned Pippy’s comment at age 4 “A prime number that’s a square number? Ridiculous”, and Frances was both amused and highly impressed at a child that young being aware of the concepts, so I explained about Numberjacks.
FACT: Pippy learnt about square numbers from Numberjacks.
FACT: Pippy was motivated by Numberjacks to play with buddy blocks, and make square, and what she then dubbed “rectangular” and “tricky” numbers. “Rectangular numbers” is a term with an obvious meaning to anyone who understands “square numbers”. “Tricky numbers” turned out to mean “prime”, which is the word I then supplied to her.
I have no idea whether Pippy will be interested in mathematics by the time she gets to University age (or, for that matter, have no idea whether she’ll even want to go to University), but having a conceptual grounding at age 4 that good?
Thank you so much, Mr. Ellis!
Pippy's blog 
Thanks very much for your kind words! We are continuing to work on Numberjacks: the website will be getting a complete makeover in the next few months; more Numberjacks merchandise, inclduing a Numberjacks magazine, will be coming on stream during this year; and we hope to develop an interactive version of Numberjacks.
Feedback such as yours is very valuable and very welcome – thanks again, and all the best to Pippy!
Best regards
Chris