Don’t design at 1000 UPM.
That’s the default for OTF but it doesn’t mean we should design at that resolution. If you use a different UPM in your Glyphs file, simply use the custom parameter Scale to UPM to scale the font on export.
I never design at more than 500 UPM and have designed typefaces (e.g. JAF Bernini Sans) at 250 UPM from start to finish. I’d even ask the students to start designing at 125 UPM, I guess. Trust me, it is perfectly possible to design a good typeface at that resolution, and the big (I really mean HUGE) advantage is that it keeps you from fiddling with pointless details. And it’s still WYSIWYG as the scaling is lossless.
Think about it like that: At 1000 UPM, and a 1200dpi printer, we have a 1:1 relation of units to dots at 60pt type size (1000UPM/1200dpi*72pt/in=60pt). Maybe first ask your students to have a guess, that might be interesting. That’s not literally 1:1 in terms of contours to dots because we have hinting and dot gain but you get the picture. If we have to print our fonts in that large size to even reproduce the 1000UPM details then that’s a sign that something is wrong. If designing means making changes in our font that might (or might not) lead to a change in our printout – at typical text sizes – then something is wrong. We need a reliable relation between the source (what we work on) and the output (what we judge) for a sensible workflow.
I’d rather work with 250 UPM and then know that a change of 1 unit in the font editor will lead to a change of exactly one dot in my 15pt printout (and if we are considering changes then that’s generally true even with hinting and dot gain).
Hope that makes sense!