Parents of summer-born babies should get more power to overturn decisions to place their children in class before compulsory school age, say MPs.
The Education Committee wrote to schools minister Nick Gibb saying "summer-borns" often miss a year's school when they opt for a later start.
It heard evidence that some younger class members were labelled with special needs or subject to bullying.
The government said it would review the committee's recommendations.
Children generally start school in the September before their fifth birthday, even though they may not turn five until almost a year after some of their peers.
Many parents of summer-born and premature babies want their children to start formal schooling later than is required by local authorities.
Some fear there is an impact on the child's ability and confidence when they compare themselves with older classmates.
Academic evidence suggests that those born later in the year do not do as well at GCSEs as those born earlier in the academic year.
The cross-party committee of MPs called on ministers to ensure education authorities and academy schools offer flexibility to children born in the summer.
They had heard evidence that sometimes these younger children are put straight into Year 1, missing out on the reception year altogether.
The demands of Year 1 are very different from those of reception, when teachers are checking that children have grasped the basics of the alphabet and numbers.
This means they may end up as the youngest and smallest members of a class whose other pupils have already had a year to get used to school life.
Committee chairman Graham Stuart said: "Our recent evidence check examined issues related to school starting age.
"It was very clear that the month of a child's birth has a measurable effect on their academic outcomes and their likelihood of SEN (special educational needs) diagnosis.
STARTING SCHOOL - THE FACTS
Children reach compulsory school age in the first term after their fifth birthday
Local education authorities are required to provide for the admission of all children in the September after they turn four
School admission authorities are responsible for deciding which year group a child goes into when a request is made
There is no statutory barrier to children being admitted outside their normal age group
But parents do not have the right to insist that their child is admitted to a particular year group
"We also heard that there is a greater risk of summer-born children being bullied, and placed in low-ability groups.
"In particular, some parents find their summer-born child may be forced to start school in Year 1, rather than reception, when the child reaches compulsory school age. Even if parents think their child is not ready, they currently have no right to appeal against this decision.
"We heard evidence that government guidance for admissions authorities about summer-born and premature children is sometimes overlooked."
Where a parent requests their child is admitted out of their normal age group, the school admission authority is responsible for making the decision on which year group they should join.
The committee called on the Department for Education to undertake an analysis of which admission authorities are observing the guidance, and to consider the merits of using a child's due date rather than birth date in admissions policies.
A spokesman for the DfE said it recently revised the admissions code to make it clearer that decisions should be made on the basis of individual circumstances.
"Decisions on whether to admit a child outside of their normal age group are rightly made at a local level based on the individual circumstances of each child.
"Our school admissions code makes clear that councils and academies should take into account the views of head teachers as they may be able to tailor a child's school experience to allow them to thrive."