Amy Ellis-Simon was at a crossroads 11 years ago: She could pursue her interest in teaching—she'd majored in the history of Caribbean women's reproductive issues—or she could take a crack at the corporate world. Her father, a schoolteacher who had emigrated from Jamaica, encouraged her to explore business.

Good idea. Ms. Ellis-Simon is the head of corporate access at one of Wall Street's leading firms. As a senior sales executive in Merrill's convertible bonds group, she helped raise more than $9 billion in 2011 for U.S. companies, including prominent names like American Express and Carnival Corp.

While growing up in Evanston, Ill., she says, she never contemplated a career in finance. But she discovered that the field stirred the same competitive juices that flowed when she ran sprints for her high school track team. Through a group called Sponsors for Educational Opportunity, which prepares minority students for careers in investment banking, law and other professions, she landed an internship at Merrill Lynch in 1993. She returned to the firm as an analyst trainee the following year, after graduating from the University of Michigan with a bachelor's degree in history.

She had an inkling that things would work out for her on Wall Street following a rigorous interview at SEO, of which she's now vice chairman. The interviewer fired unpleasant questions at her, demanding to know why was she worthy of his time and why she got a B- in a statistics class. "It was like being on a trading floor," she remembers. "You were being really grilled, you had to think fast and the atmosphere wasn't always friendly. But it fascinated me, and I decided to give it a shot."

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