When installing a Windows Server 2012 server to replace an old Server 2008 I needed to access the Active Directory Schema Snap-in but it didn’t appear in the Microsoft Management Console list. It seems that the DLL for it isn’t registered with Windows so you need to do that first. You simply need to do
regsvr32 schmmgmt.dll > and then click
After you do that the option should appear in the Add or Remove Snap-ins list withing Microsoft Management Console.