Manor Green School in Maidenhead is to be 'remodelled' so that more pupils can be taken on.
The £545,000 necessary to redesign the successful school to accommodate more pupils by next September was agreed by members of the Royal Borough's ruling cabinet on Thursday.
It will be added to the £350,000 already put aside to help the school expand.
The school for children with special educational needs opened three years ago on its current site at Elizabeth Hawkes Way, Maidenhead and demand for places has increased.
The money comes from a government grant and contributions by developers, agreed when planning permissions were granted.
The plan was one of a number agreed at the meeting. More than £3m is also being made available to increase spaces for pupils in Maidenhead primary and junior schools with Ellington Riverside Primary School being allocated nearly £2m.
In Windsor an extra classroom is to be provided at each of two schools - Homer First, Dedworth Green as well as one in Datchet St Mary School at a cost of half a million pounds.
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The Met Office has issued a yellow alert for Windsor and Maidenhead, Slough and Wokingham, warning that rain moving eastwards across the south of the country may turn to snow in some places.