Recent Drug Testing Article

The article I read was a recent case called Burlison v. Springfield.  A lawsuit was filed on a Missouri school district for putting on a lockdown on the school with mass suspicionless searches and seizures because it violated the Constitution of both the state of Missouri and America. 
In the school, the Burlison siblings were a part of it.  The principal announced the lockdown and that all students should leave their belongings behind.  Then a K-9 unit came in to check out the students' bag and when the siblings came back to get their belongings, they were opened and searched.  They told their parents and they filed the suit. 
In my opinion, its ok to have a lockdown with searches but do cops still have to go through the trouble of searching through bags while all the k-9 dogs snift through the bags with the result of no drugs being found?  If I were one of the cops, if the dog gets the scent of drugs, I would open up that student's bag that has drugs.