The parent, who has not been named, contacted Professor Marshall over concerns that children's safety had been compromised by changes to free school bus provision. However, after following up the matter to determine if there were wider issues for other children, Professor Marshall has decided it would be inappropriate to take it further.
In August, the council withdrew free school bus transport for about 1,100 children living less than two miles from their school. The move was designed to save pound;238,000, and the council is charging children a fare of pound;1 per day for a return journey, or an annual payment of pound;190.
Campaigners claim some of the routes were not properly risk-assessed and say that the charges are forcing some children to walk or be driven to school by car unnecessarily.
However, Professor Marshall told the council: "While it may be frustrating for parents (and children) that the existing high level of free bus services has been reduced, you (the council) are still providing the option to travel on these routes, albeit at some cost. In that sense, safe routes to school do exist and have not been withdrawn."
The commissioner added that the council was still making provision for families on low incomes, was still going well beyond the statutory requirements, and had given her an assurance that an appropriate risk assessment had been carried out.
Councillor Frank McGee, who left the Conservative group two weeks ago in protest at its inaction over cuts, said he believed there had been such a drop in the number of pupils using the buses that the predicted savings had not been achieved.
He also claimed the council had tried to "bully teaching staff and headteachers by saying there were going to be cuts in other parts of the budget, which encouraged school staff to induce parents to take up the option of the new services".
He said that one of the local buses, which used to carry 35 to 40 children when transport was free, was now carrying between eight and 10 children.
Councillor Mary Montague, education convener of East Renfrewshire Council, said: "We are delighted that the commissioner has been satisfied by the council's position. The new school bus arrangements are working well."
However, the Save Our Buses campaign is still urging parents to fight the move to introduce charges.