Sinclair wasn’t interesting in targeting that demographic, which is part of the reason Chris Curry left Sinclair to found Acorn. And you can see the difference in the build quality of machines like the ZX vs the BBC Micro. I’m really not convinced ZX Spectrums would have lasted long with a school of, often unmonitored, children banging away at the computer.

Not to mention that the BBC Micro came with a proper monitor. Granted home users could get away with plugging their computer into the TV but buying a TV for their computer would have been an extra cost for schools.

Commodore PET is a few years older than the BBC Micro so that might be why your school has then instead?