The Stanford 9 is a multiple choice test and any foreign language teacher will tell you that a multiple choice test is not a very good measure of a student's knowledge of a language. Language skills include not simply written comprehension, which may be partially tested through a multiple-choice test, but also speaking, oral comprehension, and writing. These skills require personalized testing which goes far beyond the scope of a multiple choice test. But if the Stanford 9 test tells us little about students understanding of the English language, it tells us even less about their educational achievement. Education goes far beyond knowledge of the English language.
Education includes math, science, music, social studies, and a wide range of other subjects.
Learning is literally a foreign language to them. But the content these kids miss out on is not the most important thing. Far worse is learning that they're not expected to know what's going on. Children who listen and listen without understanding learns that they cannot understand, and may begin to believe they are stupid. They tell kids to sink or swim, as we used to do at the turn of the century.