The independent panels are frustrated by the limit. However, lawyers have warned some councils not to point out that appeals are unlikely to succeed, as it may appear the outcome is predetermined.
Classes for five, six and seven-year-olds have been limited to 30 children since September 2001. Any school that has reached this limit invariably rejects requests to admit another child.
Elizabeth Al Qadhi, of governors' group Information for School and College Governors, trains volunteers who sit on appeal panels. She said: "The situation for five-year-olds is absolutely untenable. At key stage 1, the possibility of winning an appeal is reduced to almost nil unless there is some mistake in the local authority's procedure. The appeals procedure is a farce."
Another child can only be admitted into a "full" infant class when a mistake has been made in admission arrangements or if the child has moved into the area.
But research for the Department for Education and Skills found parents still appeal for their children to join "full" classes on grounds other than maladministration.
Sheffield Hallam University researchers, who surveyed appeal panels and education authority officers, found panel members felt the system was unfair. Researchers were told that class-size limits were "the biggest issue for panel members". Some had resigned as they could not accept the waste of public money and parents' time on pointless appeals.
Margaret Morrissey, of the National Confederation of Parent Teacher Associations, said: "We have felt for a long time that a good suggestion is to have a lower class size of 25, with five more places available."
A DFES spokesman said: "Schools have very clear admissions criteria. There is not scope for introducing flexibility."