An example of a positive relationship between number of children and their education level. People really do respond to incentives!

Her parents were true pioneers and moved from Minnesota to Alaska in 1925 with Dolores (4) and 4 other children, heading to Pt Agassiz across the water from Petersburg to homestead land there-- the territory of Alaska promised to build a school house and furnish a teacher if there were 7 students-and the Ramstead family soon fulfilled the quota. Three more children were born to the Ramstead family in Alaska, all growing up on the farm.

I see a paper using this policy as a natural experiment coming up...