Agree about doubling events not required.
Also you only need touch control - as it works with mouse too. So any mouse click is a touch.
I was thinking allong the lines of 4 slots with pictures in animation frames.
Up arrow above and down arrow below slots (great for touch).
Students can cycle threw images until they feel they have right sequence.
You currently have 1 correct of 4 - this could be a blue border around slot if it is correct. and a red one if not.
That is one brain fart thought pattern.
The other along your lines is using Card is overlaping number object.
Do a check
So number(animation frame = 1) = Card (animition frame 1) 1=1 correct
number animation frame 2 =/ card animation frame 3 ||| 2 =/ 3 incorrect
The overlapping makes it easier to just drop card on other card. The whole snap to place isn't needed. makes it look more like a deck of cards that you place down on top of each other.
Well something like that???
EDIT: Damn I really got to learn to edit my writing so others can better understand. Anyways, if you don't understand anything (which I won't blame you) just shout, I'll try to be more clear.