Which counts at school--Nature or Nurture?

Interesting article in The Australian:

Genes have it over means in determining academic performance
07 November 2005

LONDON: Nature, not nurture, is the main determinant of how well children perform at school and university, according to a study to be published this week.

The researchers came to their conclusion by comparing how well adopted children did at school when they were brought up alongside parents' biological children. The relative effects of genes and the home environment were then separated out. Previous studies have suggested that the home environment, and in particular the level of family income, is the most important determinant of educational attainment.

But the new study, to be published in the Royal Economic Society's Economic Journal, will argue that while income and home environment account for about 25 per cent of educational attainment, inherited intelligence is responsible for the rest.

Doubling a family's income would have only a small effect on educational performance, say the researchers, who examined more than 15,000 children, 574 of them adopted.

It found that, on average, the adopted children performed less well. This, of course, need not be a bar to success in life. Many adopted children enjoy spectacular careers.

The research may lead some to question government policies aimed at improving the performance of poor children at school and university.

Such policies, it suggests, will work only if targeted at able children.

The study, Does Family Income Matter for Schooling Outcomes?, by Wim Vijverberg, professor of economics at Texas University, and Erik Plug, an economics researcher at Amsterdam University, concludes that previous studies suggesting a strong link between family income and educational performance were flawed.

"Children of higher-income parents probably do well in school because they inherit superior genes, not because they can afford to buy their children a better education," Professor Vijverberg said.

Adoption experts said the research failed to take into consideration other factors. Jonathan Pearce, director of Adoption UK, said: "A lot of adopted children have faced previous trauma or abuse."

The Sunday Times

My questions:

1) Were these children adopted as infants or as older children who knew they were "different" than the biological children?

2) Is it correct to assume that adopted children necessarily have "worse" genes than their biological siblings? I have a biological sister who dropped out of high school and gave up a baby for adoption, and an adopted sister who has a bachelor's degree in Biology from a Big Ten school. Mine is an anecdotal case, obviously, but it seems to belie the "average" shown in this study.

The study is not yet published, but I'll try to track it down when it is. I'd like to see how these variations have been controlled for.

P.S. I apologize if this is double-posted. My blogging widget doesn't seem to have actually posted any of the entry I've written this month, so I thought I'd try both ways.