A head teacher whose school cannot afford textbooks said the new government support was not enough to solve the crisis.
Vic Goddard is head of a trust made up of four schools in Harlow, Essex, that are struggling with energy bills.
"Unfortunately it won't get close to solving the funding crisis during the six months let alone when it stops," he said.
The government said the support package would be reviewed in three months.
Ministers said the six-month scheme would equate to a monthly saving of £4,000 for a school paying £10,000 a month for energy.