update 2012/07/13: I have realized only today that from March 2012 Scratch is also available with a GPL v2 license.
Recently there have been two separate discussions on two italian Free Software mailing lists, about the meaning and obligations of the license for the source code of the educational software Scratch. In both cases, I asked (and received) confirmation of my understanding of the license directly from the “Help@Scratch”. The discussions were about two topics that are, I believe, interesting and relevant for everybody considering usage or development of Free Software, especially (but not only) in educational and non-profit contexts. Therefore, I’m publishing the answers I got from the Scratch team here (with their approval), hoping they may be useful to everybody else with the same doubts in the future (but please see the disclaimer below!).