I'm a believer in teaching grammar in the context of writing and reading. That is, knowing certain grammatical structures can improve student reading. For example, Beowulf is written in appositional style, so knowing about appositives and appositive phrases can make the epic more accessible to students.
Knowing grammar helps students control their own writing. The idea of learning grammar to pass a standardized test is antithetical to best practices. Also, isolated grammar instruction, as an abundance of research makes clear, does not translate into improving student writing.
Rather than taking a micro-grammar approach to teaching grammar, I believe in a global approach: Teach students to correct the most common errors and teach students to learn to fix the errors in their writing.
This lesson is one teachers can teach at any time in the year. I teach it when I notice a problem with run-on sentences and/or sentence fragments.
In preparation for teaching students the Personal Style Manual, I find it helpful to teach a short lesson on punctuating compound sentences.
I introduce the lesson simply by telling students I'm going to show them a simple formula for learning how to punctuate compound sentences.
I instruct students to get paper ready for taking notes and remind them that I'll check these notes in the next grade check. I also remind them that the notes will need to be complete for them to earn credit for that item.
As students get their paper/notebooks ready, I turn on the projector and prepare to present the short lecture.
I have prepared a screencast that replicates the lesson I presented to students. Note: During the lecture, I allow students time to write notes, and I allow time for repetition of ideas and any clarification students may need.
The document Formula for Writing Compound Sentences follows the screencast fairly closely. I put these notes on the board as I explain the formula.
Some things to keep in mind that help students understand the formula better:
The simpler we keep grammar instruction, the more receptive students are to it.