Robb Elementary School, in Uvalde, Texas, where a shooter killed 21 people in May, had problems with locks on both interior classroom doors and entrances and exits to the school building, according to a report from a special committee of the Texas legislature.

Among the issues cited in the report: The building had a classroom door system that required teachers to lock their doors from the outside using a key to secure their classrooms when they weren’t in them.

But Robb Elementary isn’t alone in this. About 1 in 4 public schools in the United States lack classroom doors that can be locked from the inside, according to the most recent data from the National Center on Education Statistics, from the 2019-20 school year.

Here’s what school facilities experts told Education Week about what’s keeping schools from changing their classroom door-locking approaches.

Although the United States invested $795 billion of local, state, and federal money into its K-12 public schools for the 2019-20 school year, according to annual federal school spending data published in May, only 10 percent went toward construction, renovation, and maintenance of school facilities.

With that funding, school facilities experts told Education Week that district leaders have to decide where to use the money and which issues are most important to fix to keep students and staff safe inside the school building.

Replacing all the classroom door locks in a school building could use up a district’s maintenance budget for the school year. But not having doors that lock from the inside isn’t usually the only problem in a school building. There might be an HVAC system that needs updating or a leaky roof that needs fixing. Some school facilities experts said sometimes it’s safer or more important to fix those other issues than put a lock on a door.

School facilities experts said there’s more to changing door locks than just putting in a new locking device on a door. Schools may also need to replace the whole structure, including the door, the door frame, and the lockset, because they all have to be compatible. Schools also have to think about the staffing needed to change the locks on hundreds of doors in a school and what the maintenance will be like when locks break.

District leaders also have to think about which classroom door-locking mechanism will work best under all the building safety regulations, including fire safety codes and the Americans with Disabilities Act. Fire safety regulations require that schools have doors that allow people to have a one-motion egress, and the ADA requires that door hardware allow for one-hand operation and not require tight grasping, pinching, or twisting of the wrist.

At the end of the day, school facilities experts said that even high-tech door locking systems won’t keep students and staff safe if they’re not implemented effectively. Sometimes students and staff will prop doors open for others, for example.

Bottom line: School safety and security needs to be put into a comprehensive plan, and not just thrown together as a knee-jerk reaction to a crisis. And there needs to be shared attitudes and behaviors within the school building to follow the safety plan.