Use 8 Raspberry Pi boards linked by GPIO to build a simple server, and then 1 RPi each for terminals. For up to about 30 terminals you would only need 1 ATX power supply for everything (except the displays). This would be a quite effective system for many applications, including a class room environment. You could even take it a step further and distribute processing across the terminals as well, giving the multi threaded combined power of up to 38 RPi's per work cluster.
RPi = The best ARM based RISC OS computer around
More than 95% of posts made from RISC OS on RPi 1B/1B+ computers. Most of the rest from RISC OS on RPi 2B/3B/3B+ computers