One of the main arguments for one-size-fits-all education has long been that students who attend public schools are more likely to be integrated citizens of their community. The theory is that students who attend private or home schools will stay sheltered within their religious or social communities as adults. Students who don't will be more understanding of and engaged with the wider community.
This idea, that one-size-fits-all education promotes integration and community involvement is a theory which has been largely disproven, at least in the United States. According to a recent American literature review, "Seven empirical studies have examined school choice’s impact on civic values and practices such as respect for the rights of others and civic knowledge. Of these, five find that school choice improves civic values and practices. Two find no visible impact from school choice. No empirical study has found that school choice has a negative impact on civic values and practices." The largest of these studies found that private school students tend to be more politically tolerant, more knowledgeable about their system of government, more likely to volunteer in their community, and more politically active than their peers.
For more information about the research on school choice and civic/community engagement, have a look at this link on the Cato Institute's blog. It contains links to other studies and reviews that have been done on the subject.
Next time someone tells you that one-size-fits-all education promotes community engagement and tolerance, ask them if they've seen the data on the subject!