One of the windows refuses to display when I request it. However, everything else seems fine.

There are two typical possibilities:

First, check to see if you have a "scroll bar" displayed on the main SchoolLeader window along the right hand side Or bottom of the monitor. If you do, try scrolling up or down to see if the window comes into view. This is often the cause of the "missing" windows and is caused by a change in the Monitor Resolution from the last time you used SchoolLeader. SchoolLeader will always display the window at the exact coordinates it was last viewed, even if those coordinates are now off the screen.

If that doesn't work try doing a cold start and reboot the computer.