Dennis Giammusso had a hard time in high school. The youngest of four kids in an Italian-American family in Brooklyn, he had struggled throughout childhood with the symptoms of his autism-spectrum disorder. "I had trouble with essays," he says. "I couldn't really always understand why I felt different."

Post-high school, he dropped out of community college because he could not pass English. But he found his way into a job-counseling program, eventually ending up as a stock boy at TJMaxx and then as an elevator operator in Manhattan. The work was drudgery. "I felt like I was chained to the building," he says. "In my second year in that job, I started to be really bored. I did anything just to keep busy. I mopped the hallways!"

Then, in 2008, he found his way into Ellen Zimiles's office. The founder of a New Jersey financial consultancy called Daylight Forensic & Advisory, Zimiles is also the mother of an autistic son, Dan. "I said, You know what? I have my own firm. I'm going to be able to walk the walk," Zimiles says. "If I want people to think about Dan in the future, I have to do this. I have to bring people in."

A Changed Culture

Giammusso, a gofer, messenger, and jack of all trades at the firm, was Zimiles's second autistic hire. Her first, she describes as a "classically autistic, fairly low-functioning" woman who struggled with eye contact and communication, but had enough skills to be an office assistant. "I said, 'She's the one we should hire,'" Zimiles recalls. There would be symbolic power in it. "The other two were very nice, but we wanted to do something that would really make a difference and that would show everyone in the firm what it was like."

When the first autistic employee was hired, Zimiles invited outside experts to come in to train the entire staff. "You may feel kind of stupid if you don't know what's going on," Zimiles told her team. Then she invited them to ask any question, no matter how insensitive or poorly constructed; her promise: "It will not be held against you in any way."

Zimiles believes that meeting all of her employees where they were then helped those employees meet their new colleague where she was. And she thinks that having autistic people on staff created cultural change throughout her organization. One day, she received an anonymous note from an employee--"I still don't know who it's from," she says--saying that he or she was thrilled to work for an organization where people on the spectrum would receive such an opportunity. She believes that staff actually behaved better after the two autistic employees came onboard. "It demonstrates an acceptance of people's differences and valuing people for what they can provide," she says. There was another bonus: "People behaved better," she says. "They didn't want to be seen in front of either of those two as behaving badly."

A Changed Employee

In 2010, the publicly traded consulting company Navigant bought Daylight Forensic in a deal valued at around $40 million, and asked Zimiles to stay on. She agreed. But one of her conditions was that she be allowed to bring her early hire as well as Giammusso with her.

Both have thrived, and one recent day, Giammusso takes me on a tour of the office. "My best things are document production," he says, "and I'm like a human GPS." He is often sent to deliver or retrieve correspondence outside the office. "Once I map something out in my brain, I can always find it again." He boasts that he has been picking up new skills too--for instance, learning how to send emails. And he says that he has changed. "I was more shy and not as open in speaking to people. I was afraid I might say the wrong things," he says. "I couldn't look at a challenge and say, 'I got it!'"

Zimiles's confidence in him and his newfound job satisfaction watered long-dormant seeds of confidence his mother planted in him years ago. "She always told me: 'You can do it!' She always pushed me. She didn't let me quit. She said that I was the smartest one of her kids," he says. He smiles. "I would say that's true."

Giammusso earns just under $40,000 a year. He's saving to take his mother on a Disney cruise--next year, he hopes. In the long term, "I want to get a co-op or a house for myself"; right now, he and his fiancee live with her parents. To make extra money, he moonlights as an Avon sales rep. In 2014, he says he posted nearly $9,000 in sales, and according to the small white board above his desk, his goal for 2015 is $20,000.

I ask him for one important piece of advice that he would share with employers considering hiring people on the autism spectrum. He thinks for a long moment before offering some words that surprise me, because they have little to do with autism at all. "Take time," he says, "to listen to your employees."