"This Chicago traffic is not working," she tweeted from the road.
But the Barbadian "Stay" singer seemed excited about the appearance.
"On my way to Barrington High School in Chicago!! I can't wait to meet these kids man!! They're major inspirational life changers," the star tweeted earlier Friday.
She killed time in traffic tweeting facts about the students' philanthropic activities.
#BHS they travel to S. Dakota every year to help the people of the Native American community on the crow creek reservation! They raised.....— Rihanna (@rihanna) March 22, 2013
35K to build houses and help meet the needs of the communities— Rihanna (@rihanna) March 22, 2013
"It's one thing to be fashionably late. This is just rude. Our lives don't revolve around a pop star," one student told the Chicago Tribune.
But students who waited hours for Rihanna to show up quickly forgot their frustrations when she finally arrived and offered them concert tickets -- even if she only stayed for 16 minutes.
Her fans, nearly despondent minutes earlier, greeted her with wild applause and Beatlemania-type screaming.
"Thank you guys for coming and waiting," she said.