In Newtown, Connecticut, a gunman shot his way through the front entrance to an elementary school and went on a rampage, killing 20 students and six teachers. At Columbine High School in Colorado two students opened fire, killing 12 students and a teacher.
They're images we will never forget and events that make security a top priority for local school districts.
"We believe in being prepared," said Conroe ISD Director of Communications Sarah Wood.
With the region's explosive growth, new schools are under construction. From Conroe, where two new campuses will open next week, to Houston ISD, where more than two dozen new campuses will be built in the next six years.
"Providing a safe environment that's conducive to learning is our top priority so we really believe in the layered approach," said Wood.
Conroe hired Houston architecture firm PBK to design its new campuses, using new security concepts. The company describes the approach as a circle of protection, from the street out front to the classrooms inside.
"We're fond of the term 'layers' because layers of security is what improves that reaction time," said Ian Powell, partner at PBK.
The distance from the street to the school's front door is longer. That gives staff extra time -- even just 15 seconds extra -- to assess any threat on the outside and lock down the building. As someone approaches, they're being watched by surveillance cameras. During school hours, a guest must be buzzed into the building.
"When you walk in the door you will probably have already been visually identified as someone coming to the door and assessed as to whether you are a welcome visitor," said Powell.
"At that point they'll approach the receptionist desk and they'll receive a badge," said Wood.
A district may choose to add break resistant or bulletproof glass to doors. PBK can design safe rooms throughout the building that are reinforced, but still look like any other classroom to an outsider.
"Students and instructors can go to those specific rooms that are particularly hardened," said Powell.
"I don't think anyone would have envisioned as recently as 10 years ago the kinds of challenges we face today in keeping our kids safe," said Daniel Bankhead, GM of HISD Facilities Design.
As HISD began designing its 28 new schools, the district brought in security experts and local police departments to meet with architects. Together, they've designed different methods to protect the inside and outside of each campus.
"People get screened before they get access to the building, and even once inside the building many of these buildings will have layers where sections can be screened or closed off," Bankhead said.
The new building designs aren't just about cameras, hardware and safety features. Previously, administrative offices were clustered at the front of the building. Many of the new designs move those offices to different parts of the campus.
"That adds a layer of supervision, a layer of awareness, another set of eyes out there," said Bankhead.
HISD is spending more than $17 million on safety and security alone at all of the new campuses approved under the 2012 bond project.