Children exposed to passive smoking are likely to do worse at school than their peers, research suggests.
Exposure to even low levels of tobacco smoke in the home was linked to lower test results for reading and maths.
The greater the exposure, the worse the decline was, the US Children's Environmental Health Center team found among nearly 4,400 children.
The findings support calls to ban smoking in public places, they told Environmental Health Perspectives...
I was ok until that last paragraph. I think the tobacco merchants ought to be assigned to sell their wares in the heart of Fallujah, but the assertion that this study supports a ban on smoking in public places assumes causation. The study only showed correlation, it wasn't designed to show causation. There's a very strong inverse relationship between IQ and longterm adult smoking, but the evidence suggests that the IQ is primary. Since IQ (the test result that is) is strongly influenced by heredity, and perhaps secondarily by uterine environment, it's hard to imagine this study could really account for those affects.
I'd bet that they've discovered an unsurprising correlation and that cessation of smoking in the home would not increase test scores. (However a better uterine environment due to smoking cessation might make a difference -- but that's not passive exposure. Intrauterine smoking is a direct exposure.)