I don't have a teen yet, but my son is 11 & high functioning autistic. We homeschool him & use an iPad for the majority of his schooling. There are many apps that utilize math skills. Numerous literature apps for books & reading. Science & place studies. He watches programs on things that we are studying at the time, which leads to another aspect, then another, and before you know it the subject has changed entirely.
Honestly, it's most like going back 200 years to slate hand held chalkboards(as far as showing your work, making notes, writing answers goes) except he has a whole world of knowledge & reference material on it too.
Current events, word meaning & usage, culture, social aspect, commerce, laws & rules, etc.
And the fact that it's fast & light & instant.
Probably the only thing I dislike is the inability to lock certain screens & apps during certain times. For self study periods, I have to trust that he is doing X & not tempted by Y(games). That or seperate user accounts like(gasp!) Windows. I hate to say I don't trust him, but he is only 11 & has issues with impulsivity related to his DX, so putting him in a candy store & telling him not to touch anything except the veggies while I'm gone is just asking for it!