Some sell direct, some don't, and some are part of companies that have an integration division.
There are some neat options. I would just say if you do look at this seriously, that you ask a lot of questions and look at multiple companies, because what these companies do can be very different.
Some for example just have people sitting there and staring at monitors.
Others use triggers from alarm and video systems to do popups / alarms and that sort of thing. Some do talk-down, some don't. Some do virtual guard tours. And so on.
I won't mention any specific company names - biased.
Jim, many of those services sell direct to end users, so integrators are not likely fans :)
Another one of these is DDT.
Most of these guys specialize in retail (like the above) or commercial monitoring (like car dealerships). I am not sure who out there specializes in schools or whether schools would be attracted to remove monitoring (there could be privacy concerns, issues with students and faculty / unions, etc.).