The head teacher of Trinity School in Carlisle, Alan Mottershead, said Josh Thomas had made a good, warm impression at the school.
Mr Mottershead said:
"He was a good lad and got on well with everybody."
Josh moved to Cumbria from South Wales in September 2010 when he was 15 and stayed for one year to take his GCSEs.
Mr Mottershead said Josh had always said that he wanted to join the Army.