The following article informs us that the Oklahoma school event is not an isolated one, but that these types of drills are happening all over the U.S.Kids All Over America Are Being Put On Buses And Sent To Alternate Locations During School Terror Drills
As you'll see when you read the article, these drills go beyond just emergency preparedness planning. Students are instructed to play injured, parents are told not to contact the schools, and students are told not to contact parents. This is typical of all mock terror drills, whether the theme is aliens, UFOs, terrorism, intruders, war, murderers (all of which have been enacted.) The message is the same: cut off from family.
The article notes that in some cases, parents were told where their children were being taken, and, they were notified beforehand. Often parents are not notified at all. In some cases however parents are not told where their children are being taken. And in one Pennsylvania school, a letter was sent to parents informing them of the upcoming relocation drill. Point for them for letting parents know beforehand. Well, except for this:
"... no child will be released for any reason during this practice activity or real emergency."
Other schools have similar policies.
A good article with a chilling overview of drills of various kinds, including one New Jersey school where a shooter broke into the school. Terrified teachers and children did their best to deal with the situation. Of course, it was fake, but neither teachers nor students knew that at the time.