I don't think we should assume that too many of the homeschooling parents are certified teachers (or are they?). Now obviously one doesn't necessarily need a degree to be a good teacher, particularly when one is only teaching one or a handful of children and discipline etc. is not an issue. But still, it is a disadvantage for most home-schooling kids, one would think. On lower levels - primary school, I suppose - the content of the classes is basic enough that most halfway educated parents shouldn't have much trouble with it, but for high school curricula this becomes rather less evident. In some cases one can rely on textbooks to a great extent, but if one has to teach one's children foreign languages without being good at them oneself, it's far from easy. Same with more advanced mathematics, physics, or other sciences. I suppose one could cooperate with other parents that may have different strengths, if one has the luck that there are homeschooling parents with the right competences in the vicinity... although then that starts to look rather like a mini-school.