I still haven't figured out how these American "grades" work. How old is the average 10th grader? I'm assuming it doesn't directly correlate to the NZ Year 10, which is populated primarily by fourteen year-olds. Unless IronTomato is fourteen, but I'll never know, because I can't be arsed to check.
Also, why is it starting in August? (September?) Why not at the start of the year, like sensible education systems?
The typical American begins 13 years of compulsory education (with caveats, many don't complete it and drop out in high school) at the age of five (sometimes six). The first year of schooling is called Kindergarten, and was formerly little more than a glorified day care for part of the day that taught a few extremely basic skills such as the alphabet and counting, hence why it doesn't have a number. Nowadays, the cirriculum is quite a bit more advanced (early childhood education in general is far more advanced than it was when I was a small boy, with Sesame Street and other preschool programs covering shockingly sophisticated subjects such as set theory, gravity, and verb tenses), and K students generally go the entire day.
As for starting at the end of summer, our school system is still locked in an agricultural paradigm, with students off school during the summer months (not even ten years ago, school didn't start until the second week of September, now many start in the third or second week of August) because that was a very busy time in old-timey farming (global warming has shifted the growing season a bit, so it no longer matches up), and nobody would have even considered sending kids to school when there was critical work to be done. Starting after the summer closure reduced the amount of forgetting.