As noted on the Hardwire LLC website, the armor is rated NIJ 3A, which will in carefully controlled conditions stop a majority of pistol bullets and shotgun blasts. However, this armor class will not stop intermediate-caliber rifle rounds as small as .223 Remington, much less have the desired effect on more substantial rifle rounds.
The whiteboard concept, allegedly inspired by the massacre at Sandy Hook Elementary School in Newtown, CT, would not have stopped or even slowed down the shooter in that instance. He was armed with a rifle chambered in .223 Remington that would have sliced through the armor.
I would not claim that the Hardwire LLC armored whiteboard is entirely useless; it might buy first responders another few seconds as the shooter figures out the device is an armored panel, and adapts to overcome its limited protection. In very limited instances where a shooter is not hell-bent on mass murder, it may buy another second or two for them to reconsider their course of action.
But primarily, the whiteboard serves to provide peace of mind for those who prefer to not think critically about how an actually shooting event would likely unfold.
Real school security — or security anywhere, for that matter — only works when active and passive systems work together to mitigate threats. The best single defense against a potential active shooter is still the presence of another human being on-site armed with a firearm and equipped with the knowledge and training of how to use their weapon effectively. This generally means on-campus law enforcement, armed security guards, or armed staff.
Only lethal force is proven to stop active shooters. All else provides little more than an illusion of safety.