Please note: I'm Canadian, I graduated high school in the Canadian system a year ago so my experiences with curriculum might be different than those elsewhere. (I'm assuming that this video is regarding the education system in the United States)

I think the biggest problem in my experience with high school was that the system is too standardized for the 'average' student. If I may be so bold, I'd claim that I was somewhat above average for the time with regard to math and science. As a result, these classes were really easy for me; but on the other hand, I was rarely if ever, learning any new information. Why bother going to class learning how to apply Newton's laws of motion for the bajillionth time when I can stay at home and learn how to program. (My school never offered programming classes)

The opposite can hold as well. If someone isn't good at a specific subject and falls behind, the matter will only get worse while the class progresses further and further ahead as 'Office Hours' don't really exist in high schools.