Grieving Dunblane parents demanded the government clarified its pledge to help following the 1996 massacre, a newly-released letter has revealed.
Teacher Gwen Mayor and 16 of her pupils were killed when Thomas Hamilton opened fire on them on 13 March 1996.
The school heard reports that ministers would use public donations rather than state funds to rebuild the gym where the attack happened.
The government later met the £2m cost of refurbishing the gym.
It was torn down days after the massacre at Dunblane Primary School.
Prime Minister John Major and Scottish Secretary Michael Forsyth were among a delegation of state officials to visit Dunblane after the attack.
Mr Major confirmed to the head teacher that finding government cash for the project “would not be a problem”.
Gerry McDermott, spokesman for the school board of governors, said that the gesture “was a source of great comfort” to the community, “relieving strain from those most closely involved”.
In a letter to Mr Major on 27 March 1996, released by the National Archives at Kew, Mr McDermott wrote: “Such an apparent change of heart and broken promise is a cause of great distress in Dunblane.
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“I, on behalf of the school board, look to you to clarify in writing exactly what the government will do.
“If there is no intention to fund the rebuilding of the gym, as you promised, this requires to be clearly stated so that the community knows where it stands.”
He said that if claims of Mr Forsyth’s U-turn were true, he wished “to put on record my extreme disappointment in the manner in which this bereaved community has been manipulated, maximising media opportunity, yet failing to deliver a widely reported promise of assistance”.
Mr Forsyth, responding in a letter the same day, told the governors there was no truth in the suggestion, adding: “I simply cannot understand where the report came from… we stand by (the) commitment.”
The Scottish minister – now Lord Forsyth – also conveyed his regret that the board decided to ask Mr Major for assurance directly before approaching him.
He wrote: “A phone call to my office would have clarified the misapprehension.”