It's not entirely obvious that comprehensive education is the right solution

That headline is to put it somewhat mildly of course. One problem with truly comprehensive education, where all do attend the same school, is that there's sometimes a minority who really don't want to be there. And who will make this blindingly obvious through their behaviour. Now, true, they do still need to be educated. However, the point and purpose of comprehensive education, the actual underlying moral argument, is that it is better if we are indeed all educated together. And this isn't true so this study says:

A large and growing literature has documented the importance of peer effects in education. However, there is relatively little evidence on the long-run educational and labor market consequences of childhood peers. We examine this question by linking administrative data on elementary school students to subsequent test scores, college attendance and completion, and earnings. To distinguish the effect of peers from confounding factors, we exploit the population variation in the proportion of children from families linked to domestic violence, who were shown by Carrell and Hoekstra (2010, 2012) to disrupt contemporaneous behavior and learning. Results show that exposure to a disruptive peer in classes of 25 during elementary school reduces earnings at age 26 by 3 to 4 percent. We estimate that differential exposure to children linked to domestic violence explains 5 to 6 percent of the rich-poor earnings gap in our data, and that removing one disruptive peer from a classroom for one year would raise the present discounted value of classmates' future earnings by $100,000.

That disbenefit of having the disruptive pupils should obviously be considered against whatever are the social benefits of all being in it together. But given that immense difficulty anyone has in making sure that one of these disruptive pupils does not in fact disrupt we're really pretty certain that this is not considered. It should be.