I think you are trying to tie IP address to a specific MAC address, is this correct? I ask because DHCP is dynamic which is the opposite of static - so not possible to have static dynamic.
Your options are:
1) Leave DHCP turned on in the server and have all clients setup to receive IP config directly from server. As is.
2) Leave DHCP turned on in the server but statically setup the clients to use a specific address from the IP range (preferably outside of the DHCP IP range - generally x.x.x.65 - x.x.x.100)
3) Turn off DHCP from the server and assign all IP configuration details directly on the client.
4) Use the Hostnames and Addresses Server-Manager panel to tie the workstations MAC addresses to a specific IP address. Option only becomes evident after naming the specific host (choose Local).
I think the fourth option will give you what you are trying to achieve.