'multicultural classroom instruction is undermining children's ability to read, write and reason'

tsuwm, did you mean multicultural, or multilingual? Everyone seems to have responded on the multilingual front, but I initially read your question as wider than that.

For me, multicultural education means teaching about various cultures, and equally importantly teaching with sensitivity to the beliefs and traditions of those cultures. I think that's a good thing. I think it's useful to know how major religions differ - I think it's even more useful if an education points out how much major religions have in common! (I realise using religion as an example may be strange in the US school environment, but in many cases it's hard to separate religion and culture, and anyway the same point would apply.)

'they claim that social goals now dominate academic goals in the reading curriculum'
At the risk of being incredibly cynical, haven't social goals always dominated? One of the purposes of education has always been socialisation to the existing norms. Learning the piano and how to do watercolours for the upper class Victorian era lady. Classes to teach orphan girls sewing, cooking and housemaid skills, while orphan boys learned trades. Preparation for life after education.

Perhaps part of the 'problem' is that we no longer have one generally accepted idea of the social goals that our education system(s) should be upholding. That's multicultural in that more than one set of values is accepted as valid. And I think that's probably good overall, even if it does lead to debate and tension.

Remembering that I am still thinking in a monolingual teaching environment (with the exception of lessons in 'foreign' languages, of course), I see no necessary connection between multicultural teaching and a lessening in children's ability to read, write and reason. Spelling, grammar, logic and mathematics are all independent of whether there is a God, whether pork is a clean meat to eat or whether it is permissible for a girl to wear a skirt. (Or a boy to wear a skirt, for that matter!)

As for the monolingual / multilingual debate, I side very strongly with Han Suyin, who said something along the lines of
'Speaking only one language is like looking at the world through only one eye - you lose perspective.'