POD 1: Starting 1982, '83, '84, more liberal and leftie parents begin homeschooling their children because they think standard school is too authoritarian, plus it's not doing a good job preparing young people for a more free-form, post-industrial economy. In addition, learning differences such as dyslexia, ADHD, and Aspergers-Autism Spectrum are recognized a decade or two earlier, and schools are seemingly unable to really roll with the fact that different children roll in different ways.
And most importantly, when evangelical families start to occasionally homeschool their children, the liberal and leftie families stand up for them and say, hey, a religious or spiritual family has the same rights as any other family. In fact, the secular families give practical advice, Oh, yes, you can homeschool on academics and still participate in debate team, choir, track, etc, etc.
For example, in OTL no less an athlete than Tim Tebow was homeschooled in academics and yet fully participated with a local team in sports! So, just shift this timeline earlier, have homeschooling first become a "thing" among left-leaning parents (although probably never going much beyond 5%) and have these parents matter-of-factly stand up for evangelical Christian parents.
What about changes in social culture?