I believe that the main reason for the strict behaviour is to maximise learning time as much as possible. The school takes the view that many of their children are behind where they should be (due mainly to the primary schools they attended). They want them to catch up, and not just catch up, but to fly. The whole way the school operates is oriented toward that.
The goal is to maximise the learning time; the rationale is that children in private schools have advantages they never will, but one thing they have is a Spartan approach to learning. Work hard, never give up, practice.
That's a quote from a blog by Tom Bennett, after visiting the school.
It's the idea that such schools need to be set up to help black children avoid gang culture that's problematic,
Well, there are a lot of black parents who don't see that as problematic, and I don't blame them. I suspect if I were in their position, I would feel the same. When wealthy people find their children are getting sucked into a bad culture, they have other options, such as boarding schools.
However, I feel I should stress that I don't think that's part of Michaela's mission statement; it was more my own deduction from the book I mentioned earlier. Personally, I think all children would benefit from a Michaela-style ethos; but there are an awful lot of parents who disagree.
Put the poor kids in strict schools? I would like to see all schools sort out their behaviour problems, as a priority. But I suspect that many poorer parents, who are often saddled with the most chaotic schools, and who know that they don't have the resources to help their children outside of school (tutors, revision guides, financial support for extra years of study) may have more cause than I do to be anxious for their children to attend a school that maximises their chances to learn. I have the resources to pick up the pieces for my children (and I have had to do so), but others are not so fortunate.