I didn't see Dreamschool but the Twitterverse (#dreamschool) were pretty unanimous in their condemnation. One colleague at school exclaimed that she hoped people would see that no matter what you put in front of some children they'll still ignore it. My suspicion is that, in common with other "reality" shows, all will come right in the end. Careful editing will have created the worst possible first impression so that we can see how much progress these talented "teachers" will make.
Am I just a little cynical? I don't think so, it's just that programmes like Dream School need a narrative arc to keep people viewing*. In real reality, teaching doesn't have a clear-cut narrative, it's much too messy and stop-go. Lessons that go brilliantly with one class, flop dismally with another. Some classes work hard one week, then idle or bicker the next.
*Seemingly Mary Beard does not agree...we'll see...
The closest I've heard any pundit come describing why this might be is Sir Ken Robinson, who talks about organic education, by which he means... oh hell... if you haven't seen this, watch it - if you have, watch it again.