It's really doubtful that more than a tiny fraction of RPi sales have gone to kids. Be honest here, whatever the RPi Foundation's marketing, the overwhelming majority have gone to hobbyists.
The RPi is uniquely unsuited to an educational environment anyway. The SD cards are unreliable, especially in combination with the RPi's poor power filtering and the cheapo phone adapters it's usually paired with. Anyone who has used a RPi has had to deal with filesystem corruption and SD card failures, intermittent USB bus brownouts, etc, and I can only imagine the nightmare of having to maintain a lab with 50 of the things. You can't PXE boot them (let alone remote-manage them) because they have no BIOS, just a blob on a physical card that needs to be swapped out.
The Pi should have had eMMC day one, and shipped with a proper power adapter and better power filtering. But much like their choice of Broadcom SoCs - they made a political decision that they were going to market primarily around the $35 price point, and so they cheaped out on $5-10 worth of hardware and ended up with a device that was entirely unsuitable for their stated purpose.
And the terrible thing is - the PC is not the sole component in the system anyway. The Pi still needs a case, a a monitor, keyboard, switches, etc, and if you are trying to stand up a lab for the first time it's not like you have 50 monitors or keyboards laying around for free, you need to buy those. So you are looking at more like $150 per system anyway, and the $10 you save on cheaping out on the hardware becomes a meaningless fraction of the total cost. Just buy the right hardware the first time. An ECS Liva is only like $75 anyway, it comes with a case, onboard eMMC, AC adapter, and wifi, you've made up the difference in cost in accessories included in the box.
There were many other terrible design decisions as well - such as the choice of USB as a system bus, which is again entirely unsuitable, especially when you are running on a low-power processor where running the USB bus full-tilt eats a significant fraction of your CPU cycles. It's like that shitty Mac Performa x200 road-apple design with the split half-width left-hand/right-hand busses which couldn't talk to each other, it eats up all your cycles by just using your disk or network. Even if the processor on other boards is no faster in synthetic benchmarks - they have a proper system architecture with SATA and often USB 3.0 and gigabit ethernet that makes an enormous difference in real-world performance.
http://lowendmac.com/2014/power-mac-and-performa-x200-road-a...
Furthermore - the Pi was plagued by driver problems with its USB stack for years. It would randomly drop USB frames when operated at USB 2.0 speeds, and it took upwards of 2 years after launch for the Pi foundation to get around to pushing a fix (again, because they chose a processor for which they could not release documentation, and they did not employ enough staff to actually fix their issues). How on earth are you supposed to do education on it when they can't even get their system bus to be stable?
https://www.raspberrypi.org/forums/viewtopic.php?t=5249
https://github.com/raspberrypi/firmware/issues/19
https://github.com/raspberrypi/firmware/issues/9
You know what I would do if I was running an actual lab? ECS Liva Xs, or other cheapo x86 PCs running a standard stack. Or go down to your university surplus store and pick up as many generic Dell boxes as you need for $50 apiece, out the door, ready to work. The Pi is good for embedded hobbyist work (the i2c interface is very powerful), but it totally fails as a machine for teaching programming compared to Ye Olde White Box.
I tried to run a pair of RPis as my fileservers for about a year and a half, and I finally just gave up and sold them. They aren't good for the "mini Linux PC" application at all, compared to properly-designed hardware that you can buy for only a little bit more money (or sometimes even less money, especially when you work out the total system cost).
(note: Pi3s can finally PXE boot without a SD card, which is like the bare minimum requirement for running an educational PC lab without going insane)