You may have some reasons to want to lock out users from Terminal access, but maybe it would be worth reconsidering the overarching principals involved in open source learning tools and platforms.
Basically having the ability to install and even change software is at the heart of free and open software, so having access is essential.
On the other hand, countries may seek to limit control root access for major deployments. However to control access combined with reselling seems to be also sliding away from FOSS ( see: http://en.wikipedia.org/wiki/Free_and_o ... e_software
In any case, you may want to pursue your questions at more active forums such as "sugar" on IRC and read up on options at http://wiki.sugarlabs.org/go/Sugar_on_a_Stick