I'm sure this varies between states but at my school in New York we had nine periods per day rather than nine classes. One of these was taken up by lunch and th

I'm sure this varies between states but at my school in New York we had nine periods per day rather than nine classes. One of these was taken up by lunch and then science classes would often take up two adjacent periods. Most people also had at least one study hall period which could be used for homework or socializing. In the end, most people were taking six classes or so. You also had the option to take classes at the local college or do independent studies for AP courses that weren't offered if you weren't challenged enough. Nine subjects at once is certainly pushing it for most students but that definitely isn't universal in the US.