The Local Government and Social Care Ombudsman has upheld 11 complaints against Norfolk County Council, in the last two years relating to its failure to provide suitable provision for children with SEND.
The boy's mother also complained that the council offered too little support while her son was away from school.
The council has agreed to pay the family £4,000 due to the delays around the EHC plan and a further £250 for the inconvenience of having to complain.
The ombudsman's report gave the council's reason for the delays were caused by an "unparalleled upsurge" in requests for an assessment.
In a second recent ruling, a boy who had been excluded from his primary school was reported to have missed out on eight months of education. In his case the council took 26 weeks to produce his EHC plan, meaning he was not appropriately supported.
The council has agreed to pay his family £3,500 in recognition of its failings and for the inconvenience caused to the family.
Norfolk has also agreed to pay for a £400 dyslexia report, which the boy's mother commissioned.
In addition, the council has promised to provide a laptop and technology assistance to the pupil, which is highlighted as needed in his EHC plan.
In his ruling, ombudsman Michael King revealed that in the last two years nine similar complaints have also been upheld against the council.
The council has also agreed to carry out a number of reviews on how to improve support for children with SEND, including ensuring EHC plans are completed in good time.
It has also agreed to look at ways of providing alternative education for children out of school as well as an audit of children who are missing from education in the area.
"We have issued a focus report on out-of-school education provision for children, and on councils' use of Education, Health and Care Plans, and expect councils to use these to scrutinise, learn from and improve the services they provide to children in their areas," said the obmbudsman Michael King.
"In both cases these children were without the vital support and provision they needed at crucial times of their education. I hope the remedies the council has agreed will go some way to repairing the damage done.
"We welcome the proactive steps the council is now taking to improve its provision and oversight of services for children with SEN, and hope this will ensure children will get the support they need in future."
A council spokesman said that requests for EHC plan assessments have risen from 172 in 2014 to 1,060 last year.
"We fully accept the LGO's [local government ombudsman's] findings and have already complied with all recommendations from both reports," he added.
"Like many authorities we have faced unprecedented increasing demand for EHC plans, with requests more than doubling over three years, but we have clear plans in place to address this."