In this paper, we consider a packet scheduler exploiting multiuser diversity in a wireless network with AMC (Adaptive Modulation and Coding), and propose a packet level performance model based on the effective bandwidth theory to investigate the joint effect of the AMC and the multiuser diversity scheduling on the scheduler performance. Based on our performance model and analysis, we investigate the packet level performance behavior of the scheduler. Numerical studies are also provided to show the usefulness of our packet level performance model in the design of the packet scheduler. Keywords Packet Scheduler