A group of head teachers have said they have no confidence in Birmingham's school transport service for children with special needs.
They wrote to the city council after some pupils were not picked up from home and others dropped off at the wrong school.
A petition has been signed by more than 280 people demanding answers.
Kate Booth, cabinet member for children's wellbeing, "wholeheartedly and unreservedly" apologised.
Denise Fountain, chair of the Birmingham Special Schools Head Teacher Association, told the Local Democracy Reporting Service transport for many children had been "complete chaos" at the start of this academic year.
She said some schools had themselves picked up children who had been missed and head teachers simply had "no confidence" in those organisations managing the system.
Parent Mary Riddell, from Great Barr, said the bus did not turn up on her 11-year-old daughter's first day of term and she received "zero communication" about it.
Mother-of-twins Charlotte Bull, from Rednal, who set up the petition, said she was "absolutely sick" of the "sub-standard provision".
The city council said at the start of term a "very small number of pupils were transported to the wrong school by home-to-school transport providers" and an investigation would take place.
'Exceptional let down'
A spokesman for the council said home-to-school transport had run "smoothly" for the vast majority, but was aware there had been "some issues".
Councillor Kath Scott, chair of the overview and scrutiny committee that oversees Special Educational Needs and Disability transport, said it was an "exceptional let down".
"Children cannot get to school and are missing their legal right to an education," she said.
"We need to take this way more seriously, and take action more swiftly."
Ms Booth said: "I really do not underestimate the emotional turmoil this failure in service has created, and can only apologise on behalf of the service, and say we are acting as quickly as possible to resolve the issues."