I have been trying to get this to work for years, without success. And then recently I tried it again and lo and behold it worked like a dream!
Part of the problem was that if the day was even slightly humid the gold leaf electroscope wouldn’t hold its charge.
Secondly it had to be charged negatively, and I was never sure if I was charging it positively or negatively.
Thirdly I didn’t realise that I had to sandpaper the zinc in advance to remove the oxide layer.
Fourtly I don’t keep a list of questions related to demonstrations which I can’t get to work, so I only remember that there is a problem when I go to teach it each year, instead of asking an expert.

And I apologise for stating that this is “the most important least impressive experiment in the history of science”. It is actually rather impressive.
If I do say so myself.