Concerning the AP Seminar extended writing, Solo teachers can help students with critical thinking.
This includes evaluating strong and weak points of arguments, the causes of problems, and potential solutions to problems (including the strong and weak points of various solutions).
It is difficult for students to develop arguments 1) within paragraphs and 2) between paragraphs.
Solo teachers can help with this "coherence" by showing students how to develop ideas more fully within paragraphs, and how to link ideas from one paragraph to another and from one section to another.
Students also need to improve on their capacity to use readings in their essays, including how to read other arguments for strong and weak points, and how to compare different articles to each other.
Other things to consider: bias, addressing counterclaims, using convincing examples, challenging common assumptions.