OD User list not populating

We've got a lab of Macs, running 10.5.5, and an OD server running 10.5.5 Server. The computer turns on and the user list populates the screen. That student logs out and then it shows that network accounts are available, but the user list is not populated. Logging in with "Other" works, but with 5 year olds, that's no the best bet. Any ideas?