Southfield School For Girls in Kettering had to close and send its 1,000 pupils to sites around the town for seven months because lethal asbestos was disturbed during refurbishment work at the school.
Pupils lost coursework, teachers had their notes destroyed and all the school's computers were ruined because of the work that took place in the summer holidays in 2003.
The refit eventually cost £6.5 million and a civil case is still to be settled.
Northampton-based Briggs & Forrester Electrical was fined £60,000, B&W Asbestos Removal Specialists, of Bedford, £30,000 and its director
Marcus Buckle was fined £10,000 after admitting breaching health and safety rules.
Issuing the fines, Judge Richard Bray said: "Work involving asbestos has to be carried out in a very careful manner to avoid the spread of contaminating dust.
"It's clear in this case the work fell well short of the standard required – so much so school staff complained.
"The school had to be closed for two terms as a result of the problems, with all the distress and inconvenience that caused"
The defendants were also ordered to pay £45,000 costs at Northampton Crown Court.
Briggs & Forrester had been employed to carry out £40,000 of electrical work at the school.
The project included the removal of 240 ceiling tiles insulated with asbestos, which was sub-contracted to B&W Asbestos Removal Specialists.
The court heard B&W failed to make sure the area was sealed off correctly and tiles were broken and dust spread into corridors and classrooms.
THE Health and Safety Executive has issued a warning about the dangers of disturbing asbestos following the Southfields School for Girls court case.
In summer 2003, asbestos ceiling tiles at Southfield School, Kettering, were removed as part of work to upgrade the school's electrical system.
During the works, asbestos dust was released into the air, posing a danger to workers and cleaners at the school.
Pupils were not at risk as the work was undertaken during the summer holidays but they were unable to return to school until the following Easter.
Health and Safety Executive principal inspector Richard Lockwood said: "Asbestos can be a killer if disturbed, but if contained and well managed poses minimal health risk.
"More than 500,000 non-domestic premises still contain some form of asbestos, posing a real threat to maintenance workers.
"They could drill or cut into the material, causing exposure to deadly fibres."
Southfield School was closed for six months while decontamination works were carried out. As part of this process, the school lost coursework, teachers' notes and all its computer equipment due to potential contamination.The school was refitted at a cost of £6.5m.
Chairman of governors Christopher Groome, said: "It was very traumatic for the school and it is a sign of our strength that we came through the loss of our buildings for a major part of the school year and held together so well."
Former student Lynsey Green, 19, of Collyweston added: "I was doing my GCSEs at the time and it had a big impact on us – I hate to think what it was like for people doing their A-Levels."
Briggs & Forrester Electrical managing director Paul Burton said: "We regret the incident and as a consequence we have imposed new procedures to ensure that similar occurrences never happen again."
No-one from B&W Asbestos Removal Specialists Limited was available for comment.
A civil case in relation to the incident is still ongoing.