How to determine the current Active Directory or Exchange Server schema version

To check the forest schema version:

dsquery * cn=schema,cn=configuration,dc=domain,dc=local -scope base -attr objectVersion

The command prompt will return the Schema version:
56 = Windows Server 2012
47 = Windows Server 2008 R2
44 = Windows Server 2008
31 = Windows Server 2003 R2
30 = Windows Server 2003
13 = Windows 2000

To check the domain schema version:

dsquery * cn=ActiveDirectoryUpdate,cn=DomainUpdates,cn=System,dc=domain,dc=local -scope base -attr revision

The command will return the revision of the Active Directory update:
9 = Windows Server 2012
5 = Windows Server 2008R2
3 = Windows Server 2008

To check the exchange schema version:

dsquery * CN=ms-Exch-Schema-Version-Pt,cn=schema,cn=configuration,dc=domain,dc=local -scope base -attr rangeUpper



Taken from http://support.microsoft.com/kb/556086