My oldest son has a great friend who goes to the public school across the street. Ever since she started kindergarten, she'll come over to play after school sometimes. Once I had to get something out of her backpack and peeked in her homework folder to see what kind of homework 5-year-olds get. The stuff was on par with what I was teaching my son, so I was relieved.
Now whenever any school kid comes over, I ask if I can see their homework folder and they are always happy to show me. I have to say I do see a difference between what they teach at the Catholic school up the road and in public school. The private school kids go to private school for a reason. They are advanced in what they are doing by at least a grade level over public school.
Keep in mind that quite a bit of what all kids learn will be gone from their brains by the time they graduate. That goes for homeschooled, unschooled, private schooled, public schooled, TV-schooled, and whatever.