Some simple questions for perspective:

What is a digital conversion:
A digital conversion is a simple replcacement of the recording device to change the recording method and data storage format.

Is a digital conversion complicated?
No it simply requires the customer service person to unlock the existing VCR lock box, unplug the main power harness and unplug the camera inputs, then remove the VCR, insert the DVR into the place the VCR was and then plug the power and camera inputs into the DVR or adapter cable if needed, close and lock the lockbox and you have converted the VCR based system into a DVR format. The only variation will be adding 2 self tapping screws on the ATX systems to mount them inside the existing VCR lock box. In reality it take me less time to do this described process than it takes me to tell one how to do this. Approximately 2 minutes or less is what it takes me to do the conversion myself.

Is digital conversion expensive?
This is a relative question and depends entirely on the perspective of the school system. It currently costs about 2 times the cost of a new VCR. In the short term it cost more to convert to digital. Every year it is getting less expensive and I believe the DVR will be the same price as the VCR within 5 years.

Why would someone want to change out their VCRs for digital DVRs?
DVRs require almost no maintenance at all,
"CF" card system have no moving parts to wear out
No changing tapes every day, no cleaning record heads, no more tapes to buy.
DVRs record for months with no interaction by driver or administration.
DVRs can provide video data into your PC for simple transmission and archival.
DVRs can support up to 8 cameras.
Digital video offers greater flexibility in enhancement when needed.
20 years ago camcorders with 2 hour record times was a good start, currently VHS based VCR systems offer 8 hour record times, but the future is digital as the very long record times up to months, the need for almost no interaction or maintenance and the improved reliability and longer life.