The federation's regional organiser Nicole Calnan has criticised the federal government for refusing to listen to David Gonski, who attacked the Coalition's plans in a speech on Wednesday night.

"To axe the funding model from 2017 will hurt our disadvantaged students who would have benefited the most from a needs-based model," she said.

The Coalition scrapped the final two years of the original six-year Better Schools funding agreement in last week's budget.

The final two years were to deliver the bulk of the funding but instead it will be indexed to inflation from 2018.

Funding analysis by the Teachers Federation, based on 2013 notional figures from the federal Education Department, revealed public schools would lose about $29 million in the Cunningham electorate, $35 million in Throsby and $35 million in Gilmore.

At Barrack Heights Public School, Gonski funding has led to the creation of two alternative learning classes, an Aboriginal education program and an orienteering program.

"It helps children develop their literacy skills in a range of ways by engaging them," Ms Calnan said.

"In the orienteering program they use a compass and follow directions, and eight of their students have made the state finals.

"It's helping enhance their real-life literacy and numeracy skills."

Illawarra president of the NSW Secondary Principals' Council Belinda Wall said the federal government had breached its commitment to Gonski made while in opposition.

"The fear is the funding will be below the real costs of running a school," she said.