Graham Pearce came up with the cash after the previous owners of Haresfoot Senior School in Berkhamstead, Hertfordshire, announced in May it would be closing at the end of the year.
Like many of the parents of its 70 pupils, he felt the pound;2,600-a-term school offered the best education for his 10-year-old son Miles, who suffers from a rare form of autism known as Asperger's syndrome. This condition makes social interaction difficult because while the child is fluent in language, they interpret everything very literally and find it difficult to relate to their peer group.
Mr Pearce, a 47-year-old businessman (nappies and advertising) and entrepeneur from Watford, said: "My wife and I researched every alternative for Miles and decided there was nowhere better for him to start his secondary education next year.
"Without falling into the special needs category, the school is unusual in providing a good education for youngsters who, for a number of reasons, are not suited to large mainstream schools.
"I never wanted to own a school but when I heard Haresfoot was going to close, I decided to use every ounce of my 30 years of business experience to save it."
In less than four weeks, Mr Pearce raised pound;1m worth of investment from parents, friends and the local community, and secured a loan for the rest of the money from a charitable trust.
Haresfoot occupies a grade 2 listed property built in 1911.