Hipmama and Terrie have a very valid point. When the govt says 1 million kids are homeschooled, it's to be taken with a lot of salt grains.
You probably have another 50K who are "underground", they don't report to the govt. for one reason or another. There tend to be more underground hsers in states like PA and NY where the laws are stiffling, but there are plenty here in FL too, where laws are fairly lax. You have those who want to avoid or protest the strict laws as well as those who just don't want to report what they are doing to the govt - but that's another issue for another day.
You also have the kids in some states who are taught at home, but are not considered homeschooled by the state. For instance, here in FL you can enroll your child in a private school (aka umbrella school) that takes care of recording keeping for your schooling. They collect the bare minimum paper work (attendance report, birth certificate and shot record) and they let you do what you want. Even though the child is taught at home by a parent with parent chosen materials, by law the child is considered a private school student - NOT a homeschooled student. In FL there are approx. 35K students enrolled in this type of private school, so that adds quite a few to the govt numbers.
You also have kids who are taught at home, but use public school programs, such as charter schools. The curriculum isn't decided or directed by the parent. In some states this is still considered homeschooling, in some it isn't. There are hundreds of thousands of kids in schools like this in the US.
You also have correspondance schools, which work a lot like the FL umbrella schools.
In some states, CA is one I think of off hand, homeschooling doens't even exist by that name. It's called an IEP or private school or something else.
So, I think when the govt says 1 million homeschooled it could be as muchas 50K-100K off in either direction. It depends on what each states considers "homeschooled" when they report.
Meg