Despite billions of dollars that have been poured into hardening schools nationally, 1 in 4 U.S. public schools lack classroom doors that can be locked from the inside, according to a survey conducted two years ago by the National Center on Education Statistics, a federal research office.

The safety feature is missing in much of Texas: 36% of the state’s schools said they did not have interior-locking doors in the majority of their classrooms, according to a 2018 survey commissioned by Gov. Greg Abbott. Outdated locks are especially common in older school buildings that haven’t been renovated, industry representatives said…

The Robb Elementary teacher and her colleagues had been instructed to keep their classroom doors closed and locked at all times, using keys that they were required to carry with them, she said. But that system created frequent opportunities for mistakes: Each time she and her class returned from lunch or from the bathroom, she said, she had to use her key to unlock the door handle — and hope that she remembered to relock it again before going back inside.

Once she was inside, the teacher said, there was no way to confirm whether the exterior handle was locked.