Knut Harms informed me about the electronic materials for learning GanttProject which are available in German here:
http://www.schulprozesse.de/content/view/87/1/
Materials are free for personal use. I don't speak German but Google Translate did a good job and translated this page.
PDF file is available on this link:
http://www.harms-oldenburg.de/schulprozesse/component/option,com_docman/task,doc_download/gid,45/Itemid,33/
