I think it is obvious that it is possible for some home schooled children to far exceed the mean achievement levels of those schooled in public establishments (to use the US phrase).
What none of us should lose sight of is the point of the original post. Home schooling is used by those with narrow agendas, often moulded by religious views, as a mechanism to restrict the exposure of their young ones to a diverse education that encourages critical thinking skills. Home schooling has gained some traction with Witnesses who think they are doing the best for their kids. They think they are providing them with the right level of knowledge, equiping them with just enough education to support a life of full time service to Jehovah (a.k.a the org). They think they are helping them avoid unwholesome influences.
The reality is that they are producing young adults who are at a high risk of not having good critical thinking skills, are ill equipped to deal with life choices outside of the scope of narrow WTS goals and are condemed to perpetuate the prejudices and logical fallicies of their parents.
Having said that, there are plenty of traditionally schooled Witness kids in exactly the same boat.