The secondary in Rossendale, which did not wish to be identified, has helped four pupils continue their studies while they served jail sentences over the past three years.
But staff were particularly impressed by the two Year 11 boys, sentenced to four and eight months at Stoke Heath young offenders' institution for their role in a burglary in 2000.
The school decided that both pupils should stay on its roll, and provided them with books, work-sheets, and mock exams. The boys' then deputy head said she had initially experienced frustrations persuading prison officers to pass on materials, but that the boys had studied enthusiastically.
Teachers prepared the boys' classmates for their return, and the teenagers were back at school just two days after being released.
The school has since had similar success with a girl who served a sentence in a women's prison and a boy who went to a young offenders' institution last year for an assault involving chemicals from a home-made bomb.
The former deputy head, who now works for a council's pupil reintegration service, said: "Ironically, most of those pupils probably got better grades because they were so bored during their sentences."