We were still using 5 1/4”, but the school CS teacher had a special press that cut a notch into the 360K (?) ones to trick the Apple II’s into using them in 720K mode.

She also had a utility to copy original software disks onto the “high density” disks, then read back the data.

From what I could tell, it worked like a charm. 10% of the copies failed, but whatever.

(Coursework was stored on unmodified disks, of course.)

The special press was fancy! I used a hole punch (the type intended for punching small round holes in paper), and as long as you lined it up correctly it worked great.

Come to think of it, it was a hole punch.

I was envious of a friend of mine with a ZX Spectrum +3A, with the builtin drive.

The rest of us had tapes.

And yes the high school computers were running MS-DOS 3.3, with two 5 1/4" drives and no hard disk.

+3, not +3A.

I suspect you're thinking of the Amstrad Spectrum +2 (grey, largely the same as the Sinclair ZX Spectrum 128) vs Amstrad Spectrum +2A (black, contained a +3 motherboard minus the FDD controller, and less compatible with external peripherals).