According to data tracking African-American representation, the percentage of black partners doubled in the early 2000s, then began sinking in 2008 as law firms adjusted to the recession’s fallout on their business. Minority lawyers were hit particularly hard by layoffs. Like the low percentage of black law firm partners, black associates — who accounted for 4 percent of all firm associates last year — have seen their share of the law firm jobs stagnate in recent years.

The hierarchy of law firms does not suit everyone, said Mr. McMillian, a graduate of Indiana University School of Law, but he says his law firm went out of its way, “from Day 1,” to provide him with the mentoring, experience and relationships needed to become a top-performing lawyer. Barnes & Thornburg, which has 600 lawyers, has nine African-American partners, up from four in 2004 when Mr. McMillian joined the firm.

“I had challenges, including developing my technical skills, and juggling my family responsibilities,” said Mr. McMillian, the father of twin sons born prematurely. “When I came to the firm, I had to learn to develop relationships with people internally.”

“There were cultural barriers,” he added. “I had gone to majority-white schools, but I hung with the people I knew so I never had to develop close relationships with other groups. I quickly realized that in a law firm, your livelihood depends on more than just the work.”

The lack of cross-racial relationships that knit lawyers into teams to handle high-pressure client legal tasks is part of what knocks some blacks off the partnership track, said Deborah L. Rhode, a Stanford University Law School professor and director of its Center on the Legal Profession.

Black lawyers operate in a profession that is one of the country’s least racially diverse, she said. Bureau of Labor Statistics data, she said, shows that some 88 percent of lawyers are white, which is higher than most other professions, such as physicians and surgeons whose composition is 72 percent white.

As part of the research for her newly released book “The Trouble With Lawyers” (Oxford University Press), Professor Rhode surveyed the managing partners of the 100 largest law firms and the general counsels of Fortune 100 companies, most of which said they placed a high priority on diverse employment — but the numbers of nonwhite partners and associates remain stuck at the low levels.