I am new to this forum also. I am not an English as a foreign language teacher or an
ESL teacher. I have taken languages though, studying German, Latin, and Coeur d'Alene (a Native American language of a tribe for which I work.) I often pondered the question of whether grammar should be taught explicitly, especially to U.S. children for whom English was their mother tongue. I began to see the value of it, though, as I began to learn other languages and even as I try to hold a conversation with my husband who could "never get into" learning anything about grammar and didn't understand its worth.
The grammar is the armature, or skeleton, on which the words hang. It lends meaning to the words and understanding to the sentence. Without understanding the structure of the language, you can only progress so far. Children in school come with a basic understanding of the language they have learned. They can carry on a conversation and get by fairly well until they need a more sophisticated understanding of conventions to gain better meanings. Proper grammar helps simplify conversations. The speakers can get a much clearer communication and avoid the extra explanations of "What I meant was..." "Did you really say what I thought I heard? Or did you mean something else?" and so forth.
Sooo, I believe that at some point some explicit teaching of grammar is necessary and desirable, whether you are teaching a conversational class or a more formal writing or communication class.