The design watchdog has agreed that the grade II-listed building, which has an unusual engineered roof, should be knocked down in part, a move that is key to a Future Systems plan to build a new school.
There is a strong argument for the demolition of parts of the school, which is regarded by Lambeth Council as failing and has been placed in 'special measures' by the government.
Future Systems is nonetheless attempting to retain some of the best elements of the Elephant and Castle school, including the pentagonal assembly hall, which will be restored as part of the construction work.
This decision will be welcomed by Lambeth, which is promoting the changes, and English Heritage, which is backing the plans.
A statement from CABE said: 'We support this proposal in overall terms, and think the scheme is an intelligent response to a complex brief and site.
'We welcome the work done with English Heritage to put forward a convincing PPG15 case for partial demolition of the listed building, and hope the spirit of close collaboration continues.
'The principle of building a simple three-storey U-shaped teaching block to the Deverell Street boundary is sound. The proposal appears to be a successful piece of architecture that combines old and new in a convincing way,' the statement adds.