Given that some states do not require standardized testing I am not sure how you can compare.

But forget about test scores and rankings - they mean little or nothing in real life. By that I mean no one cares if you got an A or a D in Biology in the 6th grade.

It would be interesting to get a fair cross section of home schooled adults and see how they compare themselves to classroom educated adults of the same time period. It would also be interesting to see if they have chosen to home school their own children.

Another bit of information: in the US home schooling can take many forms including education in the home, in a group of homes, partially in home and a classroom, with a curriculum and testing, without a curriculum and testing. Hard to compare apples to oranges to pears.