The Thorny Question of Teaching Grammar
When I’m dealing with second language learners who have a good grasp of grammar, then I can use the grammatical rules to explain the punctuation, although usually people who can talk about subjects and predicates already know where to put the period.
Those of our learners who speak English as a first language already know English grammar. You can tell they know grammar because they never say things like “I the dog kicked,” or “I saw very old two men.”
However, they usually cannot talk about grammar. It seems to me that by first teaching people how to recognize a noun and a verb, then introducing the idea of subject and predicate, we build a very shaky foundation for teaching where to put the periods. I’d rather use the methods outlined above, and short circuit the grammar lesson. Basic literacy learners need to know where to put the period long before they tackle talking formally about grammar.