A teaching union is urging the government to carry out a survey of all schools to check whether potentially life-threatening asbestos is present.
The Association of Teachers and Lecturers (ATL) wants asbestos to be removed from all schools by 2010.
The substance, which causes serious diseases of the heart and lungs, was widely used between 1945 and 1975 when thousands of schools were built.
Schools are legally required to check for asbestos and manage any risk.
"This is the tip of the iceberg"
ATL general secretary Dr Mary Bousted said her union was deeply concerned about the continuing risk to teachers, support staff and pupils from asbestos in schools.
"There is still too little information about asbestos. We don't know how many schools still contain asbestos, so most teachers have little idea of whether they or their pupils are being exposed to it.
"Schools should keep and maintain asbestos registers to record the locations and condition of any asbestos, and let staff know."
She added: "Over 400 ATL members know they have been exposed to asbestos in their school or college.
"But this is the tip of the iceberg. Many teachers and pupils will be unaware, and because asbestos related illnesses take between 15 to 60 years to develop it is difficult to know how many will become ill or die as a result of exposure."
Exposure to asbestos can cause mesothelioma which is usually fatal, lung cancer, and asbestosis which can be fatal or highly debilitating.
Health and Safety Executive figures suggest at least 182 people working in education died in Great Britain between 1980 and 2000 from mesothelioma alone.
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