A good speech therapist will encourage a bilingual student to continue learning her home language when she is at home. The mother and father should take a strong lead in engaging the child in that language that they feel the most proficient in. A strong lead. A strong example of language usage.
At school we will teach the child in English, and the child will become fluent in both, eventually. This still amazes me. It is like a magician's trick. I will reach my hand into this hat and pull out a cute little brunette girl that can spit out any English idiom that your little blond sister can! And she will do it with confidence and certainty.
But we will never ask the parents to only use English at home. These kids need to hear a lot of words. They need to be read to. They need to be talked to. By mothers and fathers who feel good about their own culture and language. So please, no apologies about the lack of English at home. You help with the flooding of your own words, and I will help with the flooding of mine. And your child can build the boat all by herself.