This article was reproduced with the kind permission
of the British Broadcasting Corporation
23 November 2007, 10:59 GMT
The pair, aged 15 and 17, who cannot be named because of their age, admitted setting fire to Darwen Moorland School in Blackburn in July last year.
At a hearing at Preston Crown Court, both were sentenced to two years and eight months youth custody.
Det Con Mark Oates said the cost and disruption of the arson was "enormous".
"The judge has imposed a severe sentence on these two youths," he said.
"The cost and disruption to the school at the time was enormous but thankfully the school was able to rebuild and put the incident behind them.
"The result will send a strong message to the public that offences of this nature will be thoroughly investigated and robustly dealt with by the court."
The school is due to become an academy in September.