Nine school buses have been ordered off the road after serious mechanical defects were found.
The discovery was made during a five-day operation at Blair Drummond Safari Park, near Stirling, while pupils were on day trips.
Officers from Central Scotland Police checked the buses while pupils were visiting the park.
The most serious defect found was an emergency door which could not be secured shut
Braking defects, a faulty exhaust, oil leaks and a broken seat belt were among the other defects found.
In addition fifteen drivers were found to be working in excess of their hours or unable to prove the hours they had worked.
Sergeant Bob Murphy, of Central Scotland Police's Collision Prevention Unit, said: "The buses were checked while pupils were inside the safari park and those with the serious defects were immediately taken off the road. The operators then had to find an alternative buses to collect the pupils once their visit was over.
"Bus companies are given the responsibility of safely taking pupils to and from school and on school outings. It is extremely worrying that nine buses were so defective they had to be removed from the road with immediate effect. We want to reassure parents that we will do everything we can to make sure their children are traveling on buses that are completely roadworthy. We will continue to address this."
Road policing officers also carried out checks on buses transporting pupils to local high schools.
Six were found to have minor defects and were given time to have repairs carried out.
The checks were carried out between Monday, June 18 and Friday, June 22.
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