Upvote:6
Thanks to comment from @MJeffryes
School children, who are visa nationals, and, are resident in an EEA country do not need a visa if visiting or transiting the UK as a member of an organised school group.
To qualify school children must:
be accompanied by a teacher have their names included on the officially approved ‘List of Travellers’ form.
Schools must get the ‘List of Travellers’ form from the foreign ministries of the EEA country where the school party is travelling from. The European Commission website provides contact details.
... now there's just the next thing to sort which is the fact that the planned trip straddles the possible UK crash out date! But that's another story ;)