More than three quarters of teaching staff will be sacked from NSW prisons under a new education model approved by the NSW government and expected to be rolled out across the state's prisons by early next year.

The decision to slash teaching staff from 152 full time positions to just 20 comes as the NSW prison population skyrocketed to a record 12,390 inmates in March.

NSW Corrective Services Minister David Elliott. Credit:Geoff Jones

Corrective Services NSW currently employs 158 teachers across the state's prison system, all of whom will be affected by the cuts. They will be forced to reapply for the remaining 20 proposed positions under the new model, while the delivery of education and training courses will be outsourced to specialist training organisations.

Deputy Secretary of NSW Teachers Federation Maxine Sharkey said the 158 teachers were advised on Tuesday they would be flown to Sydney on Thursday for a briefing with NSW Corrective Services Assistant Commissioner Dr Anne-Marie Martin to discuss their options, including voluntary redundancies.