Spoken like someone truly unaware of how children think! You should work in education, there's plenty of people like that there.
The child could in fact become horribly confused about multiplication because of a bullshit technicality, and this could set them back months. Or the child could be certain they're right and this breaks trust in authority -- non-obedient children are not inherently bad, but without careful handling they can become extremely aggressive.
I certainly relate. In fact, you can fairly easily identify, in all these comments, who has experienced similar BS and who is knee-deep stuck in theory without understanding the human component behind it (looking at you, pohl).
The child doesn't see the -1 and think "Oh, I immediately understand why my answer is wrong! Of course, I understood 3 groups of 5 instead of 5 groups of 3!". No, the child sees it, thinks "but you told me they're the same? ok...", and is now more confused than ever about what's actually been taught in the class. Most 9 year olds don't know how to introspect.
Urgh. The comments here are so infuriating because this complete disconnect is exactly the same as the one the people behind the design of the most atrocious curriculums and methods have! Damn it, who here is actually taking into account their own age compared to the kid? (And fun trivia: It's the same belittling, disconnected behaviour people have when they talk to 18-22 year olds about life experiences they can't reliably have had before the age of 35... except it's a lot more flagrant here)
