Well, I’m not one to quit on a problem like this and I’ve now come up with exactly what I want. Try downloading this PDF document and opening it in Adobe Reader. (The only limitation of this approach is that it does need Adobe Reader – not Mac Preview or Chrome’s built-in PDF viewer etc.)
Anything not coloured black in the PDF file is clickable! Click on any of the blue expressions to hide them. Click on the red ‘hide’ eye to blank all the expressions together. Click on the green ‘reveal’ eye to show all of the expressions.
Moreover, you can choose to print the document either filled or blank (and the eye icons don’t appear on the printout)! Students could even use the PDF file to test themselves in a similar way to flashcards.
The beauty of this approach is that the solutions can be revealed in any order, at any time (unlike say a Powerpoint where the order is pre-determined).
If you’d like to see behind the scenes, I’ve shared the source for this document on Overleaf.