Mybus vehicles are used for dedicated home to school services to primaries and secondaries in areas such as Leeds and Wakefield.
But a consultation, which ends on March 15, is testing whether the scheme represents "value for money" after local authority budget cuts.
West Yorkshire Combined Authority (WYCA) said it was engaging with schools, parents and other interested parties on 20 primary school services.
The authority today said that "in the vast majority of cases", other public transport options will be available to users.
One parent who relies on the P53 service, which has 13 to 14 regular users, to get her eight-year-old child to Methley Primary School is concerned about losing the scheme.
A WYCA letter she received, seen by the YEP, reads that the service "does not meet the Combined Authority’s value for money criteria" and "as there are suitable walking or public transport alternatives for the journey to and from school", the authority is planning to withdraw the service from September 1.
Mum Angela Barker said: "The public transport options they have given are laughable, as the distance they cover is a fraction of the distance to school and could be walked quicker than the time it would take to wait for the public bus."
The authority has recommended the family use the 410 and walk from Church Street or the 189.
She added: "Schools are inundated with cars surrounding them on a morning and ours is no different and parents are forever being asked to find alternative transport.
"However the alternative we have been using is now under threat of removal and so as a working parent I will have no option but to take my daughter to school by car once again."
The mother-of-two, who has used the service for around 10 years, thinks that it is not adequately advertised and that the consultation period is too short.
A spokeswoman for WYCA said: “The Combined Authority organises and subsidises a range of school bus services for around 25,000 pupils and students across West Yorkshire.
“Reducing local authority budgets means that the Combined Authority is having to review all services to ensure they represent value for money for local tax payers."
She added: "In the vast majority of cases, pupils will have a public transport alternative."
Mybus started taking children to and from school in autumn 2004 after Metro won £18.7m in funding from the Department for Transport.
The website for transport body Metro, run by WYCA, reads: "On primary school Mybus services, for your child's safety and your peace of mind, the drivers have a list of who should be travelling on the bus and which bus stop the child is to be picked up from or set down at."
The Local Government Association (LGA) warned last year that nearly half of all bus routes were under threat because of funding cuts to local government
It said councils in England faced an overall funding gap that is expected to exceed £5m by 2020.
Faced with continuing and "significant" funding pressures, the LGA said, councils will struggle to maintain subsidies for bus routes.