I honestly think it should be done at random just as most other jobs are. With other states starting to pass laws requiring that persons receiving government assistance be randomly screened (which I think should also be done in this state)the least we should be doing randomly screening teachers. We at times don't give enough kids credit for how smart they actually are. Usually the students know whether or not teachers are using drugs. Back when I was in elementary school a few friends and myself noticed a couple of the teachers were intoxicated during school and one of them was actually keeping a whiskey bottle in there desk.
The reason I say this is if the teachers are using drugs or alcohol, how can you expect a student of that teacher to not wanna try either drugs or alcohol. Because if the teacher is doing it the students will 9 times out of 10 take the position of " you should be telling me not to do drugs when you are doing it yourself". And most likely if the teachers are doing any kind of drug or alcohol the and the students know about it they are gonna be more likely to try it.