I think some people are conflating two different issues here. Children being exposed to covid in in-person classes is a virtual certainty, and that's something every parent who chooses that option needs to understand. The back-to-school figures that track cases, exposures, and quarantines will always look terrible by those metrics, just as they would for colds and flu if anyone cared to track them the same way.
But that's irrelevant to the real question: Is covid sufficient dangerous to healthy 12-15s that reducing its severity justifies the known and potential unknown effects of this vaccine? I'm not surprised that the answer is no, because those of us who paid attention to the numbers have been saying this whole time that covid really isn't that dangerous for healthy children. I do agree with those who've said that since it isn't that dangerous, they need to stop doing things like forcing students to quarantine and closing schools based on case numbers.
People in the US (and probably elsewhere) have been demanding emergency authorization for vaccines for under-12s for what feels like forever. The holdup in doing it made me suspect that there are safety issues. This pretty much confirms that. Yes, the US went in a different directing with regard to 12-15s, but I think more and more issues will emerge with younger age groups. They're the least likely to have severe covid, and the most likely to have severe side effects from the vaccines.
I agree that parents should have the choice when the absolute risks of both options are relatively small, but I think it's important to keep in mind that we're talking about children who can't make a meaningful choice themselves. If an adult wants to risk their own health because doing so reduces the risk to others, that's laudable. An adult risking their child's health for the same reason is much more questionable. That would be true even if vaccination reduced the risk of transmission to zero, which it doesn't - not even close. Despite what some keep trying to prove by fiat, it's not clear that it reduces it at all.