Bibifatima Akhundzada wove a white Chevy Spark through downtown Modesto, Calif., on a recent morning, practicing turns, braking and navigating intersections.

“Go, go, go” said her driving instructor, as she slowed down through an open intersection. “Don’t stop. Don’t stop.”

Her teacher was Gil Howard, an 82-year-old retired professor who happened upon a second career as a driving instructor. And no ordinary instructor. In Modesto, Calif., he is the go-to teacher for women from Afghanistan, where driving is off limits for virtually all of them.

In recent years, Mr. Howard has taught some 400 women in the 5,000-strong Afghan community in this part of California’s Central Valley. According to local lore, thanks to “Mr. Gil,” as he is known in Modesto, more Afghan women likely drive in and around the city of about 220,000 than in all Afghanistan.

For many Americans, learning to drive is a rite of passage, a skill associated with freedom. For Afghan immigrants it can be a lifeline, especially in cities where distances are vast and public transportation limited. So when Mr. Howard realized the difference driving made to the Afghan women, teaching them became a calling, the instruction provided free of charge.