Ponyboy is impressed with Johnny's maturity and intelligence.
Ponyboy and Johnny spend four or five days alone in the church hiding out. For entertainment they have a copy of Gone with the Wind. Johnny enjoys the book, and this surprises Ponyboy because he did not realize how intelligent and mature Johnny really was, because he did not do well in school.
It amazed me how Johnny could get more meaning out of some of the stuff in there than I could. (ch 5, p. 76)
Ponyboy knows that Johnny is smart, but he does not realize how insightful he can be. He did not do well in school because “he couldn't grasp anything that was shoved at him too fast” (p. 76), so teachers assumed he was dumb.
The time Johnny and Ponyboy spend together brings them closer together. As they are hiding out, they read and talk poetry. Johnny is impressed with the Southern gentlemen in the book, appreciating the “manners and charm” as they are portrayed in the book. He sees a deeper, gentler side to Johnny and he is impressed.
This means that since he gets the good grades in school and he skipped a grade he should be able to understand better since Johnny isin't that smart in academics