I think it is necessary. I am an English teacher who runs a cram school. My children began to learn in the summer vacation of grade 2, and now it is three years. During this year, their English scores were very good. They can write more than 100 and recognize 5600 words. Their daily conversation is ok. Now they have begun to learn grammar. Recently, they learned the usage of plural nouns A and an, and the new nouns in their class.