In retrospect, it seems so simple:
My wife is a teacher of English as a New Language (ENL). It has also been called English as a Second Language (ESL), but the NEW designation is more accurate because, for some of these students, English is their third or fourth language.
And now I look at my less-than-polyglot self and curse, quietly; I took three different “foreign” languages in secondary school, and my fluency in any of them is arguable at best. Admittedly, this was nearly half a century ago, but I suspect I should have retained more than I actually have. Middle-school kid learning English as your third language? My hat’s definitely off to you.