How much profit is being derived from the work of children though? It seems a stretch to make a comparison with plantations/slaves. Any profit that is generated from children in school is a side-effect, not a primary goal. Though I can see this setting up a situation of perverse incentives.
I doubt this is about profit. It's more likely that they wanted the copyright so they can use services that detect plagiarism without having to get consent from the students every time.
Now they're saying it's all a big mistake. Not sure I believe it.
If that was the purpose, then I think it was a mistake, since they could get the same results with a permanent, non-revocable license, instead of demanding full copyright assignment.
