Two-thirds of those programs debuting this fall, says Apple, according to AP story:

http://hosted.ap.org/dynamic/stories/U/US_CLASSROOM_IPADS?SITE=TXDAM&SECTION=HOME&TEMPLATE=DEFAULT

Shift towards e-textbooks is jumpstarting this.
""I don't want to generalize because I don't want to insult people who are working hard to make those resources," a Burlington HS (Mass) principal said of textbooks, "but they're pretty much outdated the minute they're printed and certainly by the time they're delivered. The bottom line is that the iPads will give our kids a chance to use much more relevant materials."