I did some research by asking this question to my high school classmates, most of them gave me negative opinion towards high school life. There were complains mainly about two aspects. Having to much academic pressure and having to little freedom.
It is quite understandable that high school students are under too much pressure from getting into a decent university. School life tends to be tedious and repetitive with endless practice and test.
Also, high school students are usually banned from electronic devices such as mobile phone or computers to avoid being distracted and sometimes that can be quite inconvenient and disappointing, since everyone has different hobbies and computers can help them easily get connected to new information of specific field. For instance, students like music can search for some popular songs and singers from Internet. So, without electronic devices, students’ life is much less colorful and they sometimes feel isolated from the world outside of the school wall.