Class 12 son says English doesn't need studying. His first unit test disagrees

First unit test results came this week. Physics and chemistry fine, maths ok, English is his lowest. By a lot. His argument is that he speaks English all day so there's nothing to 'study'. Except the paper wants letter formats, a particular way of answering the literature questions, word limits. He wrote two pages for a three mark question 🙂 I don't want to add a tuition in class 12 for English of all things. But I'm also not sure he'll take it seriously unless someone other than me tells him.