The council said the Lymington and New Forest area had a particular shortage of specialist places.
In a report, officers described the proposal as a “unique opportunity” to reuse existing, purpose-built school buildings.
The report said: “The decision to create a unit both meets some of the saturated need in the locality whilst also providing flexibility as it operates as part of the primary school.
“Unlike a special school, functioning as a unit will enable the provision to both be separate from the main body of the school as required, and integrated where this is advantageous.”
The council estimates the 50 additional places would cost £1.22m a year, compared with around £4m for placing the same number of children in independent or non-maintained special schools.