Not to let reality get in the way of a good joke, but more than likley the sort who has this opinion, either does not send their child to school, or also has a problem with schools.
I love the way you opened with "not to let reality get in the way of a good joke" and then proceeded to make up your own version of reality that you liked better than the one being presented to you.
Not really a reality I prefer, just felt that the assumption that the hypothetical individual would care about school shooter drills is less likely than the target audience of the joke would assume.