They should both be tested. A child should be guarenteed a certain level of education if at all possible (barring extremely low IQ or other mental issues) in this society. Some parent who decides they never needed to learn to read so their child doesn't either should not be able to neglect their child to that degree. Reading to a 10th grade level, writing, reasonable math, history, science, etc. should never be an option. I knew about homeschooling - but never that it was so lax on what it requires from parents.
And every citizen should learn what the government requires from them too - taxes, laws, all that civics course stuff that tells you how the country you live in operates. Especially when the parents don't want their kids to know.