That was the warning Owen Lynch, chief executive of government quango BECTA - the British Educational and Communications Technology Agency - gave to last week's BETT technology exhibition.
He believes information and communications technology has been marginalised in some schools, partly because there is a lack of clear research evidence about how computers can improve results.
Mr Lynch was concerned that many schools rely on government cash and fail to devote enough funds from their own budgets for ICT.
Schools have not changed as quickly as expected due to a lack of money, the cost of equipment, and the rapid pace of technological change, he said.
He cautioned against assuming that the role of computers in education was assured. The challenge for the next three years, he said, was to prove that ICT was both educationally indispensable and affordable.
Mr Lynch said the evidence base linking ICT with improvements in teaching and learning was "fragile" - a state of affairs which now was unacceptable.
He said: "ICT is an expensive resource and we have failed to provide and articulate a sufficiently robust evidential base for its use.
"Too often we have not looked beyond increased motivation and improved behaviour as evidence of success."
Meanwhile, Charles Clarke, the schools minister, told BETT delegates that every student needed to benefit from the revolution in technology so that a computer "underclass" did not result.
Making sure that society did not get split into technology "haves" and "have nots" was a key responsibility for the Government, he said.