School children as young as 11 have been left stranded on the city streets and unable to get to lessons due to controversial changes to bus services.
That is the claim from a concerned teacher who told how buses are often driven past because they are too full to take on any more passengers leaving some youngsters miles away from the school gates.
The whistleblower alleges that as many as 70 children have been spotted crammed onto the pavement at some bus stops, which has given rise to concerns about pupil safety.
He said the problem has been prompted by the cancellation of the previous BrightBus school bus service which have not been adequately replaced.
The teacher, who did not want to be identified, said: "It seems the transition from the green vehicles of Brightbus has been far from smooth.
"If kids leave their homes in the morning with their parents thinking they are getting the school bus, we can’t have a situation where they are fending for themselves a few minutes later."
He added that parents have been called out of work to give their children hastily-arranged lifts, while teachers are often asked to wait after school hours to look after children having problems getting home.
The teacher said youngsters travelling several miles across the city from High Green to Notre Dame High School in Ranmoor have encountered problems.
While pupils travelling to Bradfield School in Worrall from surrounding areas including Stannington, Oughtibridge and Wharncliffe Side faced issues.
He said: "Notre Dame is a catholic school and takes in pupils from all over the city and Bradfield School is in a very rural area so both rely heavily on buses.
"In some cases the kids used to get one BrightBus to school, but now they are having to catch two buses on the same routes."
While he praised schools for pressing bus companies for a solution, he added "demand for buses is far outstripping supply" and called for more services to be introduced.
For two decades BrightBus transported around 15, 000 passengers a day to and from the school gates but managing director Mick Strafford wound up the firm in the summer due to 'ill health'.
South Yorkshire Passenger Transport Executive pledged to find a replacement or alternative travel for all 78 routes affected that serve 32 schools but did accept that some pupils 'will not have direct links previously provided by BrightBus'.
First also announced it has 'invested in replacing 25 of the BrightBus services'.
In a letter to schools, the SYPTE admitted "there are significant changes in pupil demand from what was expected" and indicated it is working on changes to services that are awaiting approval from the council.
In another letter, First said "demand is far greater than the figures provided by Brightbus" and is "looking into a number of possibilities that would provide extra capacity."
We contacted Sheffield Bus Partnership - a collective of SYPTE, the council and bus companies - for comment and are awaiting a response.