The boys crowded in two teams at the front of Charlene Skinner's class as they thought over the math problem that flashed on the whiteboard. "That's not right," one boy said. "It says find the slope," another boy said, instructing his classmates. Next door, in Room A114, the girls spent five minutes in Justin Anderson's science class writing down everything they know about DNA. When the assigned time was up, Anderson asked the students to share some of what they noted down. "Nobody's DNA is alike," one girl said after raising her hand. "You get it from your parents," said another.      This is how some lessons are taught at James Gholson Middle School in Prince George's County: boys in one classroom, girls in another. Advocates argue that separating boys and girls removes distractions   and sex prejudice in the classroom, taking the lead from expensive private schools and boarding schools that have relied on single-sex learning for generations. But opponents say there is little evidence that such separation works, that it can be discriminatory   and that it doesn't properly prepare students for a world that is mixed.      Some experts say single-sex classes can break down sex stereotypes  , create opportunities for students and improve test scores. Kathy Couture, an education professor at Stetson University in Florida and a board member of the National Association for Single Sex Public Education, said students tend to be more focused on their curriculum and less concerned about impressing or getting attention from the opposite sex. She said girls tend to "dumb themselves down for boys" when they are together in math and science classes.       But a report published last week by the Psychological Bulletin -- which reviewed 184 studies to compare the outcomes of learning in single-sex and mixed classrooms -- raised questions about whether there are any real advantages to single-sex classrooms.      Janet Hyde, one of the report's co-authors, said there was no evidence to support the argument that boys do better orally or that girls improve in math and science when in single-sex settings. What is more important is that separating students might not adequately prepare them for college and careers. "One of the major purposes of school is to prepare students for the adult world, and that world is mixed," Janet Hyde said. "I think we do harm to students by not preparing them for the adult world." According to Kathy Couture, what is the disadvantage of a mixed class?
Students are not interested in their curriculums. Students may be disturbed by the opposite sex in their study. Girls are often absent from math and science classes. Students have fewer chances to have tests.