fourth-form name

[Vladv1]

" ‘Showing off!’ had been in his blood as long he could remember. Joining the local school choir when he was nine, he had also taken part in various small stage shows with the Scouts, even had a modest role in a locally televised drama. His first band was the Gobi Desert Canoe Club, about which little is known besides its fourth-form name".
Mick Wall "Hell Ain't A Bad Place To Be".
What does "fourth-form name" mean?