There were enough armed police to stop the Uvalde gunman three minutes after he entered the school, a top official has said.
Steven McCraw, director of the Texas Department of Public Safety, called the response an "abject failure" with "terrible decisions" made by the on-site commander.
He reiterated his previous assertion that as many as 19 officers had waited over an hour in a corridor outside classrooms before a special Border Force team entered and killed the gunman.
Nineteen children and two teachers were killed in the 24 May attack.
Mr McCraw told a Texas Senate hearing on Tuesday: "The officers had weapons, the children had none. The officers had body armour, the children had none. The officers had training, the subject had none.
"One hour, 14 minutes, and eight seconds - that is how long the children waited, and the teachers waited, in Room 111 to be rescued."
"Three minutes after the subject entered the west building, there was a sufficient number of armed officers wearing body armour to isolate, distract and neutralize the subject," Mr McCraw added.
His testimony comes after US media said this week that officers with heavier firepower and tactical equipment had arrived on the scene much earlier than first reported - but still didn't storm the classroom.
Parents outside the school as the massacre took place had pleaded with law enforcement to take decisive action to rescue their children - some of whom made desperate calls to 911.
There was also a delay in entering the classroom while officers looked for a key. However, the door was not locked and there's no evidence officers even checked, said the Texas public safety chief.
"There's no way to lock the door from the inside and there's no way for the subject to lock the door from the inside," Mr McCraw told the Senate.
The police commander on the day, Uvalde schools' police chief Pete Arredondo, has been heavily criticised, and parents and community members have called for him to resign.
Mr McCraw told the Texas Senate: "The only thing stopping a hallway of dedicated officers from entering Room 111, and 112, was the on-scene commander, who decided to place the lives of officers before the lives of children."
He claimed Mr Arredondo had "waited for radio and rifles, and he waited for shields, and he waited for SWAT".
There was "compelling evidence" that the response at Robb Elementary School was "an abject failure and antithetical to everything we've learned [after the Columbine shooting]", Mr McCraw added.
Mr Arredondo said earlier this month that he did not order officers to hold back on breaching the building and never considered himself the commander, assuming someone else had taken charge.