So I gave him the tongs instead. Things were better, but still not great. The Punk was very stressed about this activity, and was using lots of negative language (I can't, it's hard, etc.) so I suggested we stop and try something else - to which he went ballistic and said he was going to "finish dis fing!"
So I took the tongs and chopsticks and had him use his fingers instead. And then I found out what the problem had been all along. Some of the glass stones were turning over (flat side up) when he was using the tools to place them on the page. Once they were all "correct" and flat sides down he was fine and dandy again.