Setting Default System Login Session
From K12LTSP Wiki
Though it's a simple task it gets confused with changing the default session for a single user. That being said:
Edit /etc/sysconfig/desktop to include
DESKTOP="KDE"
DISPLAYMANAGER="KDE"
if you wish to have KDE as the default desktop. GNOME is the current default and to change back simply replace KDE with GNOME or any other session you have installed, XFCE etc.
