The software's operation over your network is a function of your network's
performance.  1st Class GradeBook really doesn't even know it is on a network.
It's networking abilities are all based on shared drives which appear no
different to it than a local hard drive.  The likely causes are:

1) The problem computer(s) network cards are slow, or not functioning at top
speed.  I have come across many networks where a particular brand of network
card does not work optimally.  The same card moved to a new network/computer
may function fine.  Networking can be weird at times.  To test this, try
copying a large file, say 100 MB, both to and from the "problem" computer.  The
transfer should take 8 seconds on a 100 base T network under optimal conditions
but reality is that on most networks it takes about 75 seconds.  If your
timings are much longer then this is likely the problem.  It takes about 6
seconds to load 1st class GradeBook on a network that achieves 75 seconds on
the preceding test.  Have your networking/computer professional fix this
problem.

2) The protocol being used is not efficient for running applications over the
network.  If you are not experiencing this problem on only some clients and
not others then I would recommend looking at what protocols are being used.
Compare the network configuration on computers that work properly vs. the
computers that have the slow load times.  Try eliminating all protocols on the
problem computer except one (say TCPIP).  Re-test.  If the problem persists try
another, etc.