Much simpler is to make a spreadsheet, and print out a sheet every day or two, and then just mark off on that. You "could" put the numbers back in each night, etc.
That would mean you could easily do it with only one hand, and it would be MUCH larger, and able to have multiple columns to record counts. PDA screen is small, and you'd have to scroll with more than 15-20 students. I've programmed several progams similar to that for Palm, for inventory, etc. Paper is really more functional for this type of thing.
Just my .02