Interesting to see lots of talk about grammar lately. Here's a thread from me on why I think explicit grammar instruction is important, but not all explicit grammar instruction is created equal!
I think explicit grammar instruction is important because it helps pupils to write better sentences. Pupils often write run-on sentences, and they aren't sure where they should put a full stop. This makes their writing much harder to understand.
For me, grammar instruction is about sentence structure. It's not about pedantic 'gotchas' designed to show how clever you are or how stupid everyone else is. It's about helping students to marshal their thoughts into coherent, logical sentences.
(On that note, I am sure there will be errors in this tweet thread, because I am writing it pretty quickly. I apologise for them in advance and hope it doesn't impede your understanding too much!)
To write good sentences, I think you have to know what a verb is and what a subject is. So what's the best way to teach those? You can teach definitions - a verb is a doing word, a noun is a person, place or thing, a subject is the person or thing that is doing the verb.