Perth High School pupils from the Carse of Gowrie were left waiting in sub-zero temperatures for their school transport.
The transport company has blamed technical problems and a higher than expected level of staff absence for the issues which left pupils both late for school and coming home.
A Carse of Gowrie councillor said the number of school buses breaking down in such a short space of time was “completely unacceptable”.
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A bus broke also broke down on on Thursday – leaving children stranded for 45 minutes waiting for a replacement – as well as buses being late by about 40 minutes on Friday.
The delay happened both when taking pupils to school and home again. Financial penalties are imposed when operational issues mean a service is late or cancelled.
Perth and Kinross Council has met with Stagecoach East to discuss the issues.
A spokesperson for Stagecoach East Scotland said: “We sincerely apologise to the pupils and parents affected by delayed school journeys last week to Perth High School.
“We faced a number of challenges, including staff sickness and extremely cold temperatures impacting the reliability of our fleet. Where school journeys were affected, a replacement vehicle was dispatched as soon as possible.
“Our team in Perth have preventative measures in place to minimise the impact of the cold temperatures. The safety and comfort of our passengers remains our highest priority.
“We operate 43 school contracts each day from our Perth depot and outside of weather-related challenges, these generally operate without issue. Where issues do occur, we have an agreed communication procedure in place with Perth and Kinross Council and the school, to ensure parents and pupils are kept up to date.”
A council spokesperson said: “We understand the importance of safe and reliable school transport to pupils and their families.
“Officers met Stagecoach to discuss issues affecting school transport services, which have been attributed to higher than expected levels of staff absences and technical issues affecting electric and hybrid vehicles caused by the colder weather.
“We agreed with Stagecoach their processes will be updated so their control room staff have an updated guidance on how to respond when school buses break down.”
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Carse of Gowrie ward councillors said they have received numerous complaints from parents about the unreliability of school transport in the area.
Councillor Angus Forbes said the situation was “completely unacceptable”.
The Tory councillor said: “I had a number of complaints last week about the reliability of the service and I have passed those to the council’s public transport unit who control the contracts for school buses.
“I have also been in touch with Stagecoach myself about the issues, I have had an initial response but I await more detail from both Stagecoach and the council. I hope to meet Stagecoach about this and other bus matters in the Carse next week.
“It’s completely unacceptable for so many breakdowns to occur in such a short space of time and on the same route especially with prelims just around the corner.”