Understanding grammar is inextricably linked to good writing. In my class, students will learn the parts of speech, comma rules, and all of the apostrophe rules. We will also spend time on understanding and avoiding comma-splices, run-ons, and fragments.
I generally teach grammar on Fridays and try to use music to illustrate my points.
A note on extra help: Extra help, for many students, is necessary to understand the concepts that surround grammar. I recommend that students see me the day confusion starts, not when I announce a quiz. It will be far less complicated to gain clarity when the concept is fresh. Extra help the day before an exam should be considered practice only.