whether the parents are competent enough hasn't shown to play much of a part, i mean quite frequently home schooled children academically outperform their parents.. so even if a parent isn't good in math or science for example they could outsource that learning to someone else and the internet makes that extremely easy to do today! There are some amazing teachers on Youtube teaching everything from math and statistics to guitar lessons and earth science and a lot more. Also free lessons being offered from teachers in dozens of different universities in the US :)

Let's also keep in mind that many of the kids graduating high school in the US today are illiterate and under perform homeschooled kids academically.. that's after they were educated from those "smart teachers" with those fancy degrees lol