I use this as an introduction to teaching students when to use a comma with complex sentences. It includes the following skills: differentiating between phrases and clauses, independent and dependent clauses, and prepositions and subordinating conjunctions. It works well with middle school students because to understand this lesson, students need some background knowledge with regards to subjects, verbs, and general syntax. Also, this is not a lesson that I teach every year. I only use it if I see my students are struggling with specific punctuation issues in their writing.