Say find out what the child like, then design or find something online for such students with special needs. You could help them learn through visuals, do some match-up activities in class: pin up some pictures on the wall and ask them to match the words they have in their hands with those pictures on the wall.
 
So long they could recognize the words, they learn; and the matching up with relevant pictures means that they've got the concepts and have internalized to a certain extent.

Thank you for allowing this student to use the computer! It must be very frustrating for a high schooler to have trouble writing. Is he dyslexic or dysgraphia? Often by this age poor handwriting is due to weaknesses in spelling, thought organization, reading, or putting it all together rather than fine motor skills unless there is specific motor involvement. If he has not been tested to see why the writing is so bad, now would be a good time to do so.