Laws designed to ensure that pupils with the most severe special educational needs (SEN) are properly assessed within six months have been broken by almost half of local authorities, figures show.
The process for issuing statements to children with SEN is supposed to take only 26 weeks, but statistics reveal that 55 per cent of councils complied in all cases in the 200910 academic year.
There have been some improvements, with 67 out of 152 local authorities having a 100 per cent record, up from 46 last year. Nationally 95 per cent of SEN assessments were completed on time, up from 91 per cent in the year before.
But charities have criticised the statistics and the fact that councils are not punished for breaking the law.
Plymouth City Council had the worst record in the country for completing statements within the legal time limit - just 45 per cent were finished in 26 weeks. Officers say this is due to "staffing pressures" and delays in getting information.
A spokeswoman said not making "hasty decisions" had meant the council was more able to "get it right". So far in this academic year 66 per cent of statements have been completed within 26 weeks.
"Although the process of negotiation takes time we believe its value is shown in the comparatively very low numbers of parents that take our decisions to tribunal for review," she said.
The Lamb Inquiry on SEN earlier this year criticised the quality of statements, and said parents' experiences of the statutory assessment process are "negative and stressful".
Jane McConnell, chief executive of the Independent Panel for Special Education Advice, said: "These figures shows one of the major problems of the SEN system - there is no enforcement of the law.
"It's up to parents and the SEN community to report problems, but even then there is no "punishment" for local authorities."
Lorraine Petersen, chief executive of the National Association of Special Educational Needs, said: "Where you have a system which operates locally you are always going to have discrepancies.
"Unfortunately it means a postcode lottery and this is going to get worse. The Government wants to localise the SEN system even more."