My eldest learned English at home and French at an immersion school. He speaks like a native and I speak as much French as I can to him.
He went to an English-only school last year after four years of French school. His written English wasn't his strongest subject last year; this doesn't surprise me. His verbal expression has always been very high (probably because he didn't start French until he was four).
US-born Americans don't really understand the idea of speaking multiple languages the way that people out there in much of the world do, which is probably why you're seeing articles referencing low socioeconomic status with bilingualism. There's a huge focus here on teaching English to disadvantaged Hispanic kids (often called bilingual education, which is probably why you're getting so many search hits like the ones you described) and a lack of understanding (IMHO, anyway!) on how achieve this.
Val
