My 9 year old got his report card scores today. His percentile rank is
at 99% in math, but only 92% in English.

I think that he can do better than than on English. I got 90% on GMAT
verbal part, after just one year of living here, and he's lived in the
US for 9 years, out of which he spoke English for 6 years.

My question is how do we improve his English, given his age of 9. My
first thought is that he needs to just find something that he likes to
read about and read a lot more. I think that simply reading good books
(good as in, giving some examples of good use of the language) is
already a big help.

My second thought is maybe he just needs to find some fun club, group,
discussion forum, theater, tutor or something like that that would
somehow make him more interested in learning English. He has a math
tutor who tries to keep him interested in math, maybe we can find some
equivalent of that for English.

I never studied English formally, so I am not very experienced in such
matters.

i