My take is the principal made two errors... jumping to the conclusion that the kid is getting "too much" screen time, as mentioned already, but also reacting to Dreambox as a threat, because he knows that the further your DS progresses in math on his own, the more problems it'll cause him to try to meet DS's level. So, he chose to "advise" you on what's easiest for him... unplug DS so he stops learning.
This was actually my first thought, after getting a lille POed of course. I figure that he was not at all happy when he saw where DS was and addressing screen time/my parenting was a good way of skirting the actual issue. DS learning is a result of MY bad parenting rather than an actual concern that he was going to have to deal with.
I do think that I am not going to follow it up at the moment but will be very aware of this tactic in the future.
