@xz1224 yes, school is only compulsory until middle school. There are public and private high schools but the one you get to largely depends on your grades and if you can pass their test, often the schools lead into and determine your University choices. Certain schools are more prestigious and harder to get into than others, so think of all the stress of getting into Uni and condense it into the end of middle school, with a time limit. HS test season is infamous for how much stress students go through, cramming hard leading up to them, and if you miss the date you're basically screwed until the next year, and gap years have stigmas behind them. This plays into a ton of school manga plots, directly or to the side.
I do like the idea of keeping high school optional and giving students freedom in their lives earlier, but everything else about it? sounds like hell, specially since socially speaking you'll still be looked down upon for not going through High School. The expectation is still on students to go through up to University, and the only alternatives for those who skip High School are shitty jobs or lucky prospects most won't get.