That works at the university level (at least in Canada/US) where students traditionally buy their books. Maybe it will work out for private schools too. But for public schools, it is a harder call.

Let's say traditional textbooks last for 5 years (though I have certainly seen older textbooks being used in schools). It works out to $75 either way. On top of that, you have the purchase of a tablet. At the moment, they seem to run $200 and up (assuming non-Apple) or $500 and up (assuming Apple). The thing is, you're lucky if a tablet lasts five years. So add $40/year (non-Apple) or $100/year (Apple).

Assume 4 textbooks per year for elementary, then you go from $60/year to $100/year (non-Apple) for a 66% increase in textbook costs or $160/year (Apple) for a 133% increase in textbook costs.

High school courses work out a bit better since they use around 8 textbooks per year. So costs go from $120/year to $160/year (non-Apple) for a 33% increase or $220/year for an 83% increase.

This really isn't working out to be a cost-saver. Now toss in support costs. DTB are easy to fix and will have a relatively low attrition rate. Tablets require ongoing maintenance and there are certain failures that are expensive to fix (from what I've seen, batteries seem to last 3 years in electronics devices) or nearly impossible to fix (e.g. water damage that toasts an essential component).

I'd do more math to figure out the hypothetical costs of electronic textbooks and DTBs, but I'd really need to know what the attrition rate for the DTBs and tablets are. Number anyone?