ESCONDIDO - Kevin Stevenson can tell you exactly how to get to Bear Valley Middle School, or anywhere else in a four-county area. The high-functioning autistic 12-year-old has largely memorized Thomas Guides to San Diego, Riverside, Orange and Los Angeles counties.

But he learned the hard way that getting from point A to point B can be harder than just knowing all the right turns.

On Nov. 2, a group of up to 10 fellow junior high students is accused of teasing and shoving him aboard North County Transit District bus No. 350, stealing his bus pass and cell phone and leaving him with no way home once he got to the transfer station at the Escondido Transit Center.

Escondido school resource officer Marco Sevilla arrested four of the alleged attackers, ages 13 and 14, after an investigation. Three face misdemeanor charges, while the fourth faces a felony charge of strong-arm robbery.

But Stevenson's mother, Lisa, said the incident never should have happened and points to the inherent dangers of school-age students riding public transportation.

"I've always told him, 'Don't worry, there's an adult (driver) on board,' " she said. "But in this case, the adult didn't pull over or anything."

School, transit and police officials said such discipline problems among schoolchildren on public buses are extremely rare. Sevilla said the incident is the first assault he's heard of in 2 1/2 years as a school resource officer.

But Lisa Stevenson said she's heard stories from other parents of widespread cell phone robberies on buses, stories that either don't get reported or don't get taken seriously by police.

Transit spokesman Tom Kelleher said that drivers are instructed to turn the bus around and go back to the school if there are problems. But in the alleged assault, the driver wasn't aware of any trouble, he said.

"When you've got a bus full of students, and they're hollering and making a lot of commotion, it's a pretty tough environment to discern something happened unless someone tells the driver," he said.

Stevenson was riding the bus home from school when the group, all standing on the crowded bus, allegedly assaulted him, according to the police report. He couldn't transfer at the Escondido Transit Center because he had no bus pass. A group of high school students approached him, learned of his predicament and gave him money for the ride home.

While there aren't adult monitors on buses, Kelleher said every bus has at least seven cameras rolling from different angles at all times. However, when police and transit authorities checked the tape from the day of Stevenson's assault, the footage no longer existed, having been taped over because it was five days later, Kelleher said.

Although satisfied with the arrests, Lisa Stevenson said she's still not satisfied with the safety measures on buses for children. She said her son's example shows it's next to impossible for a single driver to keep a bus full of rambunctious students safe.

Kevin Stevenson has not taken the public bus since the incident, instead opting for a school bus provided to students with special needs. It's the only school bus provided to students at the middle school. Lisa Stevenson said she supported her son taking the public bus and doesn't like the precedent set by the incident.

"Now, he's on the school bus and the kids who don't know how to behave are still on the public bus," she said.

Kelly Prins, an assistant superintendent with the Escondido Union School District, said that while she regrets the incident, she's satisfied with the way the district, police and transit officials settled it.

"I think the issues have been addressed the best the district could do," she said.

Contact staff writer Dan Simmons at (760) 740-5426 or dsimmons@nctimes.com.