The Abbott Government cannot say where almost $30 billion in budget cuts to schools will be found, says Australian Greens spokesperson for schools Senator Penny Wright.

Senator Wright said estimates questioning late last night revealed the Government had picked a random number with no thought to the consequences.

"The best Treasury could do was say the cuts to schools would be 'something less than $30 billion'," Senator Wright said.

"When even Treasury doesn't know the real numbers - you know there's no plan behind this policy.