This one may be problematic for some. Just do what he tells you to, and with some re-arrangement, you should be able to do it. If you're still having problems read the following. What I did for the final part, where you wallplant the bench on top of the wall is I put a bus in front of me, than a rail, and then another bus. I grinded the first two, and then jumped off my board onto the last bus. It doesnt matter if you stop, as long as you do it. Then I put another bus to my left (In front of the bench) and jump onto it. Then I just got as Much speed as I could and wallplanted the bench. There are many different ways to complete this challenge.
*Located near the fornt of the School.