Mastering English requires abilities that most children don’t develop until they're pre-teens.
Johnny in Topeka can’t read, but Janne in Helsinki is effortlessly finishing his storybooks. Such a disparity may be expected by now, but the reason might come as a surprise: It probably has much less to do with teaching style and quality than with language. Simply put, written English is great for puns but terrible for learning to read or write. It’s like making children from around the world complete an obstacle course to fully participate in society but requiring the English-speaking participants to wear blindfolds.