If it's a study, doesn't that mean that you need to give consent for participation? I can't believe a school can participate in a study without getting informed consent. But maybe I'm naive.
I can easily believe that a school can participate in a study without getting informed consent from every child's parent - otherwise no school would ever be able to participate in anything! However, the study must, I think, have been approved by some ethics committee, or at the very least, there is a person running it who is responsible for its being ethically run. That person or committee would be interesting to identify.
My cynical best guess would be that, if this is not simple a lie, then it's something like:
Study organisers: Do we have to worry about children changing year group during the year?
School: Oh no, we'd never permit that.
Study organisers: Good, we'll write in that that won't happen, then.
School, later: See, it says here that children won't change year group during the year.
