The Office for Standards in Education found the Wirral Hospitals' School and home education service on Merseyside guilty of five breaches of statutory regulations.
Inspectors found a lack of clear educational direction which led to loss of entitlement for some pupils and ineffective long-term planning, while finances were not linked to priorities.
The report comes just weeks after the Charity Commission criticised Ian Price, the school's head, in an investigation into the affairs of the National Confederation of Parent Teacher Associations.
Mr Price is the confederation's past chair and is now general secretary of the European Parents Association. He was heavily criticised in the Charity Commission's report, which accused the 40-year-old organisation - riven by internecine warfare for decades - of running up large hotel bills and high expenses.
Mr Price said he was neither interviewed individually by commissioners nor asked to submit evidence. He felt much of the report was inaccurate.
The OFSTED report, based on an inspection between April 7 and 11, said the management structure at his school lacked clarity. There were no job descriptions and no effective monitoring of teaching.
The report added: "Partnership with parents and the community is weak. "
It said there was little opportunity for parents to be involved in their children's education and that there were no extra-curricular activities or parent helpers in the classrooms.
Inspectors found poor attendance with 10 per cent of pupils regularly out of the classroom and said the school did not maintain an admissions register. Little homework was set.
They said it failed to meet statutory requirements on the maintenance of a register of special needs, registering and reporting attendance, collective worship, curriculum policy and the provision of showers for use after games, which were not available for boys or girls.
However, inspectors found that the quality of teaching in more than half the lessons was good, and that it was satisfactory in almost all of the remainder.
Pupils, who are aged between two and 19, were enthusiastic about the school and their progress was at least satisfactory in more than three-quarters of lessons. They made good progress in about one-fifth of lessons.
Mr Price said: "My focus has always been to get the provision in the classroom first class and I think the report bears that out."
He said he was not sure on what evidence the inspectors had based their comments on links with parents, and added: "I have letters of testimony from parents thanking me for the work I have done."