Headteacher David Sims, 59, and three other teachers at Moat House Special School in Basildon remain suspended after more than a year, pending disciplinary proceedings.
Eight teachers were reported by police to the CPS for allegedly using excessive and unwarranted corporal punishment. The action was prompted by Essex County Council's concerns over the leadership of the school for 5 to 16 year-olds with moderate learning difficulties.
Four of them, Mr Sims, deputy head Mary Thompson and teachers Christine MacAllan and Rob Craven were suspended.
The other four teachers were disciplined by governors, but were not suspended and have since been given advice and guidance on dealing with children with behavioural problems.
The CPS formally charged Mr Sims and Ms MacAllan. Mr Sims, head since 1981, faced 13 charges of wilful ill-treatment of children. But all charges against both were dropped last week, days before a trial was due to begin at Southwark Crown Court in London.
The county council last year drafted in new staff, including an acting head and deputy, and have given the Basildon school extra back-up from behavioural and psychological support services.
Ian Pollard, senior education officer at Essex education authority, said the council had also been concerned about the pressure on pupils of a trial.
He said an investigation began after officers began to pick up a series of complaints from children. "We were concerned about the leadership in the school," he said.
Personnel services manager Peter Ayre said investigations by the governing body had been completed into the cases of Ms Thompson and Mr Craven. Inquiries into the cases of Mr Sims and Ms MacAllan had been held up until the police investigation was concluded. They will now go ahead "Over a period of time, things were taking place which we would not condone and which are not acceptable," Mr Ayre said. "Those about whom we had concerns have been suspended."
The county hopes the matter will be resolved by the end of the school year. Mr Ayre said he could not say whether Mr Sims would return to Moat House.
Mr Sims, suspended on full pay, said he was relieved children would not have to go through the trial. He faces a panel of five governors.
"There were children and adults who would have had to give evidence for both the prosecution and the defence and it would have been an awful strain for them to go through. I am glad it is not going to happen," he said.
Detective Inspector Ray Andrews, of South Essex child protection unit, said: "You have to look at the benefit to the children. At certain times you don't proceed with a case because it would be worse for the children if you did. The child is of paramount importance."