There are 5 basic elements to a tort case (
https://en.wikipedia.org/wiki/Negligence
1. Duty
2. Breach of Duty
3. Causation
4. Proximate Cause
5. Injury (Damages)
Without knowing specific facts of what the defendants knew and when we can only guess, however it appears the case will have significant hurdles to clear. There is the question of the extent of their duty, and how they breached that, but proximate causation sticks out to me as big issue. Just because the school had an opportunity to break the chain of events 2 years prior seems pretty far away from being directly responsible. There were many others who also had a chance to stop things.
The case will also no doubt have to survive quite a few summary judgements on jurisdiction. Lastly, if the hope is to get to the parent company's pockets, assuming the school corporation was setup as any one of several liability limiting forms available, the plaintiffs will have to prove fraud or willful negligence to pierce the corporate veil.
Now, considering this, it still might very well lead to a settlement within the limits of school's insurance policies... which will be a decent payday for the lawyers involved but split up 100 ways won't amount to a lot in the end.
BTW- 30% would be low contingency fee. 40 or 50% is more common especially as the odds of winning go down and the costs of all the experts involved is not trivial either...
I don't know squat about tort cases in the EU but why aren't talking more about the particulars of a case against Lufthansa in a European court?