To answer those who argue that grammar teaching is necessary, I would like you to engage in a thought experiment.
Imagine that I am having a party. There is music, snacks, drinks and many guests. All of the guests are my friends. I am delighted when you arrive.
"Hi! I'm so happy you could make it! Here, have a drink! Let me take you around and introduce you to some of my friends.
"This is Bob. He is a marine animal trainer. He's American and trained the dolphins in the Guangzhou Zoo.
"Here is Richard. He's a lawyer and the vice-president of the Guangzhou Law Association. He was one of my students.
"And this is Rauol. He is the manager of the golf course, he's from Holland.
"This is Helen. She's the Southern China manager for Cambridge University Press. She is from Hubei.
"Here is Zhou Jing. She is the general manager of Microsoft Technology Center in Guangzhou. She was one of my students and improved her English very quickly so she could attend a big Microsoft meeting in Seattle.
All of these are real people I know as friends and/or students.
OK, now a question. Who is Bob?
Maybe you don't remember.
I agree that a brief introduction to a grammar form, just like a brief introduction to someone at a party, is not going to hurt unless you mix up all the people you met. But I don't think it really does much to help you really know the grammar or be able to use the grammar.
You don't really know Bob. You don't know that the secret of his job is "hunger". You don't know he is from California. You don't know that he also worked in Taiwan and in Japan. You don't know that when he was in Japan he studied the ancient Japanese martial art of sword fighting and passed several tests to achieve mastery. You don't know that he lives with his lovely Chinese girlfriend who is also an animal trainer.
What if I didn't introduce you to Bob? What if you lived with Bob? What if you observed him while he worked? What if you went out to dinner with him and his girlfriend? What if you joined him as he practiced his sword technique with his Japanese tutor? Without any introductions, you would know Bob very well.
Sure, introduce me to your friends. It's not going to kill me. (Unless one of them is a killer.) But to know them I don't really need to have an introduction. I need to spend time with them, even live with them, to know them.