"Arm" teachers sounds like an active verb. If so, it's a ridiculously stupid idea. I'm a teacher. I know a great number of teachers from a large number of school districts. First, many of those teachers wouldn't want to be armed - they'd want nothing to do with guns. Second, those who would accept the guns, you'd be spending a fortune for annual training - or do you think that just handing someone a weapon who has never fired a gun in their lives is a smart idea? And, if, say this year you take them to a gun range for an hour, and they never fire it again for years, do you really expect them to be effective 10 years down the road? How about maintenance of the firearm?
If anything, simply "allow" (not "arm") teachers to concealed carry - if they go through the normal steps to get their license. I think this is a better solution than the federal firearms policy that forbids any gun from school property by anyone - a *completely* useless rule.