What is the difference between a Word or PDF document and an e-book? The answer may currently be “very little”, but it ought to be “interactivity”, and the product that has put e-books back on the map is, inevitably, the iPad.

At Twynham School in Christchurch, Dorset, pupils and teachers alike are piloting e-books using three devices: Amazon’s Kindle, Sony’s e-Reader and Apple’s iPad. So far, the results show that all three have advantages. While the Kindle and the e-Reader are proving better for devoted text enthusiasts, Mike Herrity, assistant head, says the iPad has the advantages of a high-quality colour screen and interactivity.

Although he admits that at the moment most e-books are downloaded on to a PC, he believes the ideal tool will be a reader that combines the best elements of both. “It will be a mobile device that all pupils will use with some sort of hybrid functionality,” he says.

Dedicated e-book readers, from the likes of Amazon, Sony, beBook, and iRex, have monochrome screens and are designed primarily to be small and lightweight, with a long battery life and excellent viewing comfort. They can display thousands of pages of type from a text-heavy book or novel and were originally pitched in the same way as MP3 players, offering users the opportunity to carry their entire library in a compact and easy-to-use form.

Unlike MP3 players, however, e-book readers are able to access a wealth of free, legal content thanks to the likes of Project Gutenberg, which provides out-of-copyright texts from big-name authors. People may be getting excited about Apple’s iBooks app, but Project Gutenberg has been quietly promoting e-books at zero cost since 1971.

Also unlike MP3 players, e-book readers are a disparate range of devices that are served by an equally disparate range of potentially incompatible file formats.

Effectively, there are three elements that define an e-book experience: the book itself, the file format in which it is offered and the e-book readers with which it is compatible. One of the key considerations when choosing an e-book reader is therefore the range of file formats that it can accommodate without the need to convert files using dedicated software loaded on to a separate PC.

For publishers, this means that a key consideration when choosing the format in which to publish an e-book is the range of devices on which it can be read.

“E-book was formerly a dirty word,” admits Jim Riley, managing director of e-publishers tutor2u. “Some of the big publishers are off the pace in terms of how they perceive the transition from print to digital: their digital versions are largely the same as their printed versions because that’s easy to do.”

This is to neglect one of the advantages of online publishing, he argues, which is that updating textbooks to include new developments does not involve wholesale reprinting. But he believes getting the right hardware is only the first step. The most important stage is integrating e-books into lessons. To give teachers an idea of the possibilities, tutor2u offers 50-day free trials for teachers interested in getting to grips with e-books.

“The hardest problem is getting teachers to incorporate e-books in their schemes of work,” he says. “Giving teachers a sample chapter is no use to anybody, but if you give 50 days of free use there is a chance that it will start to become embedded. Interactive e-books are one of the best ways to support independent learning.”

But there is another obstacle to the widespread use of e-books that is only likely to become more significant, and that is cost. Even the cheapest e-book readers start at around #163;100, while the iPad starts at around #163;430. Equipping even one class will be prohibitively expensive, particularly as schools are expecting to have to rein in expenditure over the next few years.

Mark Poulter, principal of Leigh Technology Academy in Dartford, Kent, had been attracted by the potential of the iPad, but when it came to trying to negotiate a bulk order he hit a brick wall.

“When I’ve compared the iPad against e-book readers that don’t have a colour screen I’ve found that it makes a massive difference to be able to see maps and diagrams in colour,” he says. “But we tried to set up a school contract with Waterstone’s and we couldn’t get any good deals.

“Surely if I want to buy 1,000 e-book readers I should be able to get a good deal, but these companies don’t seem to have anybody who can say yes.”

This may become less of an issue if prices come down, however. In this case, Mr Poulter sees huge potential in switching from textbooks to their electronic cousins.

“I can see a massive benefit in not having moth-eaten, pencilled-in textbooks,” he says. “But the key thing for us is whether the iPad is going to be popular enough for people to be willing to give them away with a mobile phone contract.”

This may sound like wishful thinking, but the precedent has been set by smartphones and the iPad may not prove to be any different in the long run. In the meantime, the next generation of e-book readers is already starting to introduce touch-sensitive screens, wi-fi connectivity, voice recording and colour displays, not to mention larger monochrome screens and ultra-competitive pricing.

The battle between the iPad and the rest may be just beginning but, although the economic downturn may prove a blip in the march of the e-reader, it looks as if the days of linear, printed books - at least for classroom use - are numbered.

What to look for

- A wide range of supported file formats is highly desirable, but be warned that the ability to load a given format is not the same as the ability to display the content accurately.

- Preferably 16 grey-levels for maximum legibility.

- Proper e-ink technology, rather than an LCD screen, will maximise battery life and viewing comfort.

- Extendable memory via an SD (secure digital) slot is as important as the amount of on-board memory.

- A zoom function and the ability to adjust font size are essential.

- Indexing and bookmarking and the ability to highlight and annotate text are also likely to be useful.

- Other features can include integral MP3 players and voice recorders as well as clip-on lights to allow reading at night, although bright-daylight reading is not a problem with e-ink devices.

- A touch-screen may speed access but image clarity can be degraded, so do a side-by-side comparison if possible.