Zum, a Silicon Valley-based company, began serving the district this school year under a five-year, $483 million contract. The company markets itself as a technology and transportation provider, offering a mobile app that lets parents track their children's bus rides in real time.

Tymeera Hicks said her 8-year-old son, Asir, who attends Green Tree School — a school for students with emotional and autistic needs — was picked up nearly three hours late on the first day of school, Sept. 3. School begins at 8:30 a.m., but the bus did not arrive until about 10:40 a.m., she said. Dismissal that day was at noon.

"They made sure he went to the bathroom and then gave him his school lunch and then put him back on the bus home," Hicks said.

The problems continued after the first day, according to Hicks, who provided time-stamped videos she said showed her son being picked up around 8:30 a.m. on subsequent days.

"Every day has been something. I've been calling, literally reporting every day since the first day of school. It's been nonstop," she said.

Yook Tiong, of West Philadelphia, said her 19-year-old son, Jose, who also attends Green Tree but rides a different route, has faced similar delays. She said he arrived late on most days and on one occasion did not get home until after 5:30 p.m.

Tiong said the tracking app was not working, prompting her to call Zum for information. "My son is not verbal. What if they dropped him off somewhere wrong and he doesn't know what's going on," she said.

Jose ultimately arrived home safely, Tiong said. She said the driver later told her there had been a fight on the bus and that police were called after the bus pulled over. "The driver had to handle the fight on her own while driving the bus," Tiong said.

The Philadelphia School District declined an on-camera interview. In a statement, the district said it values parents' concerns and is working with Zum to make adjustments. It said it reviewed on-time performance at Green Tree School after inquiries about the service but did not share the results. A spokesperson said the district would continue monitoring service at the school and make improvements as needed.

Zum also declined an on-camera interview. In a statement, the company said it experienced initial challenges at the start of the school year that were resolved within the first week. The company said "remaining issues are related to routing" and that it is working "with district leadership as improvements are implemented to support reliable service."

According to its website, Zum serves 7,500 schools nationwide and reports a 98% average on-time rate. The company also promotes its app as a way for parents to monitor their children's rides in real time. Hicks and Tiong said the app experienced glitches but improved after questions were raised about the service.

Reports of delayed routes and app-tracking failures have also surfaced in other states, including Rhode Island, Kansas and Illinois. Zum's website says performance improves as the company works with school districts to make operational changes.

"This is my son's right to be in school," Hicks said.

Questions remain about how the district selected Zum. When asked what due diligence was conducted before the company was hired, the district said in a statement that the Board of Education authorized the contract but declined to provide additional details.

"I just hope the school district could get better with this, because it has affected a lot of people's lives," Tiong said. "I just want them to get better with their transportation, getting these kids to school and showing that they really do care about these kids."