Does he like math better or does he just like doing stuff on the computer better? Can you work the computer angle in other curriculum areas.

Does he like EPGY better because he is judged by a computer not a human? If so can you make the other work self correcting?

Is writing on the worksheets a block? Would he do them faster if you scribed for him? If so, you can delink writing and content and teach them separately.

Just some ideas of possible triggers that aren't purely power struggles..