"What we've seen is that there isn't one piece of curriculum that fits the needs of every teacher," said Keith Bockwoldt, director of technology services.

Alliance College-Ready Public Schools, a group of local charter campuses run independently of L.A. Unified, also chose iPads. Alliance could not match L.A. Unified's purchasing power — when the cost of curriculum software is factored in, it paid a little more per student. But the group also reaped a benefit from buying them in smaller batches. The price fell by $50 per device in one month, merely because the iPad 4 was quickly dropping in value.

School officials in Huntsville, Ala., were concerned that Apple products were too much of a "money pit ... you've always got to buy the next thing," said Chief Financial Officer Jason Taylor. And the Chromebook, part of a Google system, was judged as too limiting for students without Internet access at home. And the district didn't want to be locked in to Google products.

"We want to give students the best and biggest screen possible and as much visibility to the curriculum they can have," Taylor said.

Huntsville is leasing HP laptops for $750 apiece over three years. District officials said they believe the laptops will be much less expensive over time than Apple devices.

Huntsville also has moved to an online curriculum in all subjects, for which it pays Pearson $200 a year per student. Textbooks are being replaced: in middle school math, for example, the curriculum is online.

More than anything else, it is the Pearson curriculum that is driving the higher overall cost at L.A. Unified. A three-year license for math and English software added as much as $200 per device to the price tag, according to documents reviewed by The Times and people close to the bidding process.

Absence of curriculum helped keep the price per Chromebook to $308 at KIPP L.A., another group of charter schools.

At KIPP, previously purchased Apple computers are valued for multimedia projects. And the iPad's touch screen is ideal for some disabled students, said Matthew Peskay, KIPP's director of technology and innovation. But lower-cost options are fine for most students and most purposes, he said.

The Chromebooks are used for supplementing instruction and remedial work. They also allow students in the same class to work at different paces, Peskay said. Teachers and schools choose which curriculum to use.

Instructors in Perris and Riverside typically use online curriculum and resources, much of it free. That allows students to use their own computers; in Riverside, that has saved the district considerable funds.

Teams of Perris educators also have developed their own lessons that incorporate technology — which may be delivered on a different kind of computer in the future.

"The device itself is a short-term thing," said Perris Supt. Greenberg. "New devices are always coming out."