Each school district in the nation may have their own way to calculate GPA, or weigh classes. As an independent homeschooler, you get to determine your own policy on calculating grades. I encourage you to do it the easy way. A different method won't give a dramatically different GPA, and so choosing the simple method of how to calculate homeschool GPA makes the most sense.
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Is this method of calculating your GPA respected by the college board? & does the method hold in either Country or State ?
I think you may be overthinking this a bit. Here's the truth - all school districts across the nation have their own way of calculating a weighted GPA. I don't recommend using a weighted GPA, and this is the simplest method to calculate GPA that I have seen. The College Board does not need to approve your GPA, they are used to seeing all the different policies that schools across the nation have. Each country, county and state may have a policy as well. As an independent homeschooler, you get to control the policy for your homeschool. I suggest that simple is best. Colleges have told me that they do not like weighted grades, because it makes it more difficult for them to assess applicants. Unless your college or your situation requires weighting grades, I don't recommend it. As independent homeschoolers, we get to choose our own policy.
Teaching driving is just one of the many things homeschool parents are responsible for. There are 10 more essential subjects to teach for your home high school to be a success. Curious?