Biological differences lead boys and girls to learn in a different manner, according to Dr. Leonard Sax, a family physician turned author. Because of neurological differences, Sax advocates that classrooms are segregated by sex.
As you can imagine, It's a controversial idea (one of the main opponents to same-sex education is the ACLU). Here is a report by Elizabeth Weil of The New York Times about an intermediate school that had began offering separate classes for girls and boys and the positive (though biased) results that it achieved:
Sax comes off as a true believer and describes his conversion experience like this: In 2000, one of his patients, a 12-year-old boy, came to his medical office. For several years before then, the boy had been withdrawn, uninspired and on multiple medications, but he had recently made a big turnaround, which his parents credited to having enrolled him in an all-boys school. Upon hearing this, Sax said to the boy’s mother, “With all due respect, I regard single-sex education as an antiquated relic of the Victorian Era.” To which he says she replied, “With all due respect, Dr. Sax, you have no idea what you’re talking about.” After visiting a handful of single-sex schools, Sax threw himself into studying neurological differences between males and females, eventually focusing on how to protect boys from a syndrome he calls “failure to launch,” which Sax often characterizes as caring more about getting a Kilimanjaro in Halo 3 than performing well in high school or taking a girl on a date.
Link (a bit long, but very interesting)