What price progress? The answer for parents who send their children to state schools for what they thought would be a free education is that it can be very high indeed. More and more parents are being asked to buy tablet computers for their children to use in class, at a cost of several hundred pounds. And the move is drawing grumbles from families on tight budgets and fuelling fears of a "digital divide" in education.

With the use of digital technology expanding quickly in schools, headteachers are keen to be at the forefront of new teaching methods that they believe will save money in the long run on equipment such as books.

Now, ahead of the new school year in September, many schools are asking parents to stump up between £200 and £300 for an iPad or other tablet for their child, or pay for a device in instalments that can vary from £12 to £30 a month, as they rush to keep at the head of the information revolution.

While their introduction is popular with youngsters, parents and teaching unions are raising concerns that those from poorer backgrounds could lose out and that supposedly free state education looks destined to come with increasing built-in costs.

Hove Park school, in Hove, East Sussex, for example, has given parents a choice of three ways to acquire iPads as part of what it calls its "learning transformation" project.

They can send their child to school with their own device, rent one from the school for a minimum of £12.40 a month, or buy one from the school, for between £209 to £300. One parent said: "I'd like to see some evidence that bringing this kind of technology into classrooms is even beneficial to how kids learn. There's an awful lot of information out there on the net that is plain wrong. I feel quite uneasy about what we might be doing to them and to teaching."

The headteacher, Derek Trimmer, has said he expects to get complaints, but insists he wants his pupils to be able "to engage with future employers as fully independent learners confident in their use of modern technologies".

A spokesman for Brighton and Hove city council said: "Hove Park school has been able to negotiate discounts with suppliers. We welcome the fact that the business plan ensures that no child is excluded from the project through inability to pay for the equipment." A survey of more than 100 students recently carried out by the school showed the percentage of children rating their lessons as good or better has nearly trebled since the introduction of the iPads, from 31% to nearly 87%."

At the Skinners' Kent Academy in Tunbridge Wells, where parents have also been asked to contribute to the cost of iPads, one parent said she was having to pay £45 a month from her modest salary for iPads for two children. "I am cross about it because I don't think we as parents were really left with any alternative. The children are ecstatic of course, but it is a lot of money to find every month and you worry that there are people in this community who really will not be able to afford it. What will they do?"

Christine Blower, general secretary of the National Union of Teachers, said: "Given that the UK continues to be a society divided along class and wealth lines, schools should not set out to exacerbate this by reinforcing the digital divide. Having to buy iPads or tablets outright, or pay monthly instalments to the school, may well be the final straw for families on stretched budgets. Schools need to be aware that initiatives which seem on the surface to be logical and progressive can leave many pupils behind.

"Often young people will be reluctant to let their school or classmates know that they cannot afford either a computer at home or to lease one from the school. If such items are given free of charge to all pupils and are maintained and repaired by the school, then that would be a one way of ensuring all pupils have the same equal access and opportunities without stigma. Education must remain a good for all and must be accessible to all. If not, huge swaths of the student population will feel disconnected from school. This will benefit no one."

Providing tablets is not an unquestioned money saver for schools. Honywood community science school in Essex gave all its 1,200 pupils a tablet computer for free, although it did ask for a £50 contribution towards insurance. The cost was estimated at around £500,000. But 489 tablets had to be replaced after a year, while four out of 10 needed to be sent for repairs.

A spokesman for the Department for Education said it was up to individual schools what policies they adopted on technology and charging parents.