A paper by right-wing think-tank Reform Scotland shows that, although some children are entitled to two years of Government-funded nursery provision, others receive just 15 months.
The anomaly is caused because Government funding for nursery provision begins the school term after a child turns three. Reform Scotland believes the issue could be resolved by a simple change to the scheme so provision would begin two years before a child was due to start school.
Alison Payne, Reform Scotland's research director, said: "Not only does the system discriminate against younger school-entrants in terms of the gap in learning, for families using partnership nurseries it can cost them over £1000."
The Scottish Government said the Children and Young People Bill would provide more hig quality early learning and childcare than ever before.