As parents in a home school, our end goal is NOT to teach. Our goal is for children to LEARN. I can teach my kids "at the grade level" and they can't learn anything.
Instead, I gave them a skill-level curriculum that required them to learn something they no longer knew about. That is why, you can choose homeschool in San Jose for your kid.
Young adults MUST learn to teach independently. When they go to college, they are expected to learn information from the textbook itself.
University lectures often complement textbooks – they are not identical. If they don't go to college, they still have computer skills or online banking or learn how to buy a car – whatever.
In high school, my kids studied prejudice and arithmetic. You study physics. I know they study the material because I give them a test.
I don't understand what the numbers mean, but I know my children's answers fit into that key decision. I was able to teach them biology and chemistry because I am an RN and I took a lot of those subjects in college, but they also studied them.
We got better at teaching them alone because I looked for them all so often. My youngest son teaches economics and is currently working on a thesis on the history of economic thought, his professor told us.