"“However, by being so long in the lowest form I gained an immense advantage over the cleverer boys. They all went on to learn Latin and Greek and splendid things like that. But I was taught English. We were considered such dunces that we could learn only English. Mr. Somervell—a most delightful man, to whom my debt is great—was charged with the duty of teaching the stupidest boys the most disregarded thing—namely, to write mere English. He knew how to do it. He taught it as no one else has ever taught it. Not only did we learn English parsing thoroughly, but we also practised continually English analysis."
Even better if you can do both!
Your final sentence seems a bit odd in that context though: Churchill's point is that Latin and Greek actually isn't useful at all, so it would follow that it isn't better to do both (i.e. study the classics as well as English), especially as time to learn them would have a huge opportunity cost, e.g. you could use that time to study more English composition instead.
(If you think they're worth learning just for their own sake then that's another matter, but the quote seems to imply that Churchill wouldn't agree.)
I was lucky, I had two or three excellent English teachers. Very inspiring and helpful. I wish I could say the same about mathematics (most of my teachers were terrible and one didn't even teach us how to do the problems)... Or my French teacher. I think we spoke better French than he did at the end. Since I spent a lot of my childhood in rural Scotland I was effectively bilingual anyway.