Evangelical Christian private schools. There is a great blog that tracks research and what data exists on homeschooling, and in this link there’s a discussion of some research into whether homeschooled kids marry and have kids differently than kids educated other ways (particularly public school kids).
In a nutshell, evangelical Christian private school attendees end up marrying before 25 and having their first kid a few years later. Catholic school attendees marry around 28-30 and have their first kid ASAP. Homeschool and public school kids have higher rates of teen and early 20s pregnancy and marriage (still fairly low in raw numbers) and higher rates of being unmarried at 39.
Without extreme religiosity, which drives most of the homeschool early marriage, homeschool family formation and childbearing is pretty much the same as public school family formation and childbearing, which is useful information for homeschoolers to have now that the extremely religious are a much smaller minority of homeschoolers these days.
I haven’t cross-referenced this with lifetime births per woman, but I suspect based on demographic patterns that this means homeschoolers and public school kids have slightly fewer lifetime children per woman and probably per man than religious private schoolers of either Catholic or Evangelical Christian persuasion.
Anyway my rapscallionate brood is going to evangelical Christian schools, I guess!