Upper level student is a student between the ages of 15 years or more and was educated at the High school or called "Matthayom Sueksa Thonpai". They grow to full maturity and interest in their own body, various glands in body are full growth. They need a lot of freedom so they conflict with parents and it causes gaps between the ages. There are expressing harsh and daydream including liking to follow as a group but development almost as an adult and lack of experiences. They have their philosophy of life but still confused to understand abstraction.
Upper-level students may add and/or drop elective classes according to the dates noted in the course schedule without penalty such as majoring in Science-Math, Arts-Math, Language-Arts, etc.
Upper Secondary schools may be called high schools, gymnasium, lyceums, middle schools, sixth-form, sixth-form colleges, vocational schools, or preparatory schools, and the exact meaning of any of these varies between the countries.