The solution to all academic problems is to back up a step.
For example, when working an alphabet puzzle, not only do we not start with the entire board, we might not even start with the entire first row, but only two pieces of that row. Introduce only two pieces at a time, taking them out and in, out and in, until the visual discrimination of a young child is sure. Then leave the first two pieces in their slots and only work the next two pieces. Next, go back and mix up all four pieces until your little one can do them without hesitation—and then proceed as before onto the next two.
This is the way you teach a child everything: how to change the sheets on their bed, or collecting the household trash, not just their own room's trash, etc. It begins with learning how just to put the sack in the trash can—and before that, a mother must teach the child how to find the sack in the cupboard.
Whenever you meet a roadblock with your child, splinter the skill down to its tiniest part and begin there, and then you shall have good success with literally everything you attempt to conquer. (Read much more about how to do this in our 12 Amazing Brain Triggers.)