I consult to a lot of Australian private schools and their best method is using VLAN's. One for staff, one for admin and one for students.
By doing this, the schools security devices can be easily setup and maintained for students, without restriction staff or admin too much.
In schools I see 4 types of traffic. Administrators, Staff (non-teaching), Teachers and students. Currently most private schools are adding in 2 new groups, Parents and Alumni. The situation starts to become quite complex.
2 scopes in DHCP are fine, but you have alot more to setup, with switch port configuration.
Agree with @voretaq7 Having 2 DHCP instances is far more effective than 2 nics in the one machine running separate subnets
First link describes a few different ways to perform a split - http://social.technet.microsoft.com/Forums/en-US/winserverNIS/thread/9ae4e7dd-f73e-4cce-bdff-5913d5961c09
Second link is the actual deployment guide from microsoft for multiple subnets
Another interesting note, most large private schools seem to use "Net Box Blue" as a filtering/firewall device, before a hardware firewall. http://netboxblue.com/
I hate the thing, but for smaller IT teams it works well.
Since it is a school project, I shouldn't really be answering your questions for you. LOL