The first year of school in America> known as kindergarten（幼儿园），usually begins between the ages of five and six. Among rich countries such a late start is very strange. President Obama believes it is an economic and social problem； his education secretary goes as far as to say that it is "morally wrong”. This statement has some support, as it is clear from research into vocabulary that youngsters from poor families enter kindergarten well behind those from rich families-a disadvantage that usually lasts a lifetime. Children from households on welfare knew 525 words by the age of three, while the children of professionals had mastered 1,116. Pre-school can help close this gap. So in a speech last month, Mr. Obama called for a partnership between the federal government and the states to expand it to every American 1730 child. It later became known that "every" meant those who come from families with incomes of up to 200% above the poverty line-equal to an income of $ 47,000 for a family of four. Some critics（评论家）say that sending children to school at the age of four does not work. The evidence suggests otherwise. For example, on March 20th new results were announced from a study of 9 to 11 year olds in New Jersey. This report found that disadvantaged children who had attended pre-school had better literacy （读写育自力）, language, math and science skills. And two years of pre-kindergarten were better than one. Some studies also follow the effects of early learning over lifetimes, such as its effect on crime rates and other factors that may eventually burden society. Critics have singled out a government scheme called Head Start, created in 1965, which provides poor households with a range of services including school-based early education. 24. The phrase “single out” in the last paragraph means ・_____