Law school rankings are sometimes disputed, so the research team checked the enrollment figures at schools with strong records of postgraduate employment. Law schools that claimed they placed 85 percent of their graduates in gold standard jobs, defined as full-time, long-term positions that require passing the state bar exam, had fewer women enrolled than men, by about 3 percentage points. The divide was even greater in the next rung of schools, where 70 to 84 percent of students found jobs requiring bar passage. The enrollment discrepancy for women was almost 4 percent below men.

In contrast, the lowest-performing schools — the ones that listed fewer than 40 percent of their graduates in jobs that require bar passage — had noticeably higher female enrollment, at 55.9 percent of students. That indicates women who graduate from less prestigious schools have fewer opportunities to be hired for their first full-fledged legal job, which can be decisive in shaping a career, Ms. Merritt said.

One reason for the gender gap, Ms. Merritt and Mr. McEntee said in the report, was that the national rankings have become so important that the 50 highest-ranked schools “increasingly stress LSAT (Law School Admission Test) scores over other admissions factors as they fight for better rankings. This disadvantages women, who have lower LSAT scores (on average) than men.”

Women score an average of two points lower than men on the LSAT, which is still the key admissions number. Since law school rankings are weighted heavily on this number, that discrepancy gives elite law schools a greater reason — all other things being equal — to accept a man over a woman.

Ms. Merritt also noted that test scores affect financial aid, which can be crucial in choosing a law school. Prestigious schools have high tuition, and generous financial assistance helps to defray those costs, which can easily reach over $100,000. Currently, there is little transparency in how law schools negotiate tuition assistance and whether there are gender differences influencing how such sums are distributed, although most schools admit that they bargain over their overall price tag.

Some law schools that found their rolls seriously lacking women students have taken active steps to recruit them. Washington University School of Law in St. Louis, for example, began taking a more active approach when its 2013 entering class shrank to 38 percent women, a drop from 45 percent the previous year.