Ain't so/is not

on page 298 Graff begins to explain that "students do not need to read models of intellectually challenging writing... if they are to become intellectuals themselves". This is an example of academic writing because he is drawing conclusions from previously discussed research and earlier topics discussed in this paper. He then transitions to non-academic writing immediately after when he begins to offer up his own adolescent experiences.

HE does this again on page 301 at the top. In a form of non-academic writing he says that street smarts are more important than book smarts and then transitions to the effect that has on the community which is academic.
i think he does effectively mix the two to create an interesting but informative piece.