I got this one after I was level 30. I went to level 30 and all my points were on CONTROL. Then I did all the exercices in the Tour (10 of them) and those I didn't A+ on I went back to the school academy to do them with Nadal.
Most of the ten challenges are really easy if you abuse the drop shot, then when the computer comes on you, you hit them with a passing shot.
One last thing, I didn't had 100% in the academy like the name states. I had 70% and had C+ in Challenge 2, 6 and 8. Challenge 10 is broken at the moment so I got no letter.
To complete challenge 10 you need to get to three games real fast, and then fail the challenge by using all your remaining strokes (You start with 100). After I fail, it popped.
If you have any questions or want recording of me doing them (not 2,6 and 8 tho lol) feel free to comment and Ill add infos definitely.