The murals also spread a positive message — themes he doesn't just celebrate for children, but actually embody in his own lifestyle.
"I'm one to practice what I preach, so I do," he said. "I don't want to be painting an issue and then not really feeling it, not being a part of that."
Operation Clean Start began in the early '90s after Howard was struck by the sight of graffiti while driving on the San Diego (405) Freeway to Los Angeles. It wasn't an uncommon site, but it hit him differently that day.
"This time it was like a cry for help," he said. "It was literally like something's wrong. It hit me hard."
The idea stuck with him back at his job at Juvenile Hall, where he brought his students into a conversation about graffiti. They had a lot to say.
He ended up surveying about 3,000 kids on the topic, including what else they thought they could be doing with their time.
Murals came up.
At first it was intimidating painting a large mural on a wall, Howard said.
A creative person with artistic hobbies growing up, he enlisted friends and a former colleague to help with the art aspect. Navigating the bureaucracy, though, "was a whole different animal," he said.
"I also just got bumped and bruised along the way," he said. "It wasn't easy."
For Howard, graffiti drags down property values, scares people and perpetrates more graffiti.
"It's unsightly — visual terrorism," he said. "It makes me angry. I think it looks ugly and I'm not talking about graffiti art. There's a difference.... Graffiti-style art or not, if it's in the community and we don't want it there, it's vandalism, plain and simple."
It took two years before Howard stopped teaching to devote himself to his organization full time. Still, the nonprofit has never been fully secure, and the last five years haven't been easy.
Grants have been harder to come by. Operation Clean Slate has had to cut back.
Uncertainty, he said, is an unavoidable risk of being in the nonprofit sector. He sees the gains of what he is doing as well worth it.
"We are competing with some causes that are just heart-wrenching, from feeding homeless people to battered women," he said. "There are all sorts of issues that are so important and yet we are, too. We are important too. We're impacting lots of kids."