HowTos for the desktop
Using KDE Plasma, GNOME, LXDE, Xfce and/or MATE together
To install other desktop environments after installation, simply use apt:
apt update apt install education-desktop-gnome education-desktop-lxde education-desktop-xfce education-desktop-mate
Users will then be able to choose any of the five desktop environment via the login manager before logging in. Of course, you can also choose to give less choices. Keep in mind that there will be several programs for the same purpose (like file managers, editors, PDF viewers...) if more than one desktop environment is installed; this might confuse users.
The use of LXDE as default on LTSP clients can be forced; see networked clients for details.
If you don't want to do installations with the default desktop KDE Plasma, you can also install with one of the four alternative desktops, GNOME, LXDE, Xfce or MATE directly.
libdvdcss is needed for playing most commercial DVDs. For legal reasons it's not included in Debian (Edu). If you are legally allowed to use it, you can build your own local packages using the libdvd-pkg Debian package; make sure contrib is enabled in /etc/apt/sources.list.
apt update apt install libdvd-pkg
Answer the debconf questions, then run dpkg-reconfigure libdvd-pkg.
The package fonts-linex (which is installed by default) installs the font "Abecedario" which is a nice handwriting font for kids. The font has several forms to be used with kids: dotted, and with lines.