What you had varied depending on the school and resources it had (and when they started on it). The BBC Micro was indeed pushed for schools when it came out (as a result of the aforesaid campaign), but my old school had an Apple ][ running for the Computer classes. Before that we had a dial-up link to a Ford mainframe of some form using an old TTY terminal.
After I left my old Maths teacher upgraded everything, but I forget what he ended up using - it might even have been IBM PCs by that point.