According to Wikipedia, "A secondary school describes an institution that provides secondary education and also usually includes the building where this takes place. Some secondary schools provide both lower secondary education (ages 11 to 14) and upper secondary education (ages 14 to 18), i.e., both levels 2 and 3 of the ISCED scale, but these can also be provided in separate schools."
"In the U.S., the secondary education system has separate middle schools and high schools. In the UK, most state schools and privately-funded schools accommodate pupils between the ages of 11–16 or 11–18; some elite UK private schools, i.e. public schools, admit pupils between the ages of 13 and 18."
"Secondary schools follow on from primary schools and prepare for vocational or tertiary education. Attendance is usually compulsory for students until age 16. The organisations, buildings, and terminology are more or less unique in each country."
Planning for secondary school is probably the most important step for the whole education planning. For pre-school and primary school education, they are just for fundamentals and foundations, and it's usually good to catch up later even if the primary school is not ideal.
Secondary school rankings and performance are the key for applying for a good college or university.
There are some tasks that have to be done during secondary school studies:
Find the best capabilities and the most interested areas.
Develop a specialty area, such as math, piano, hockey, etc. Attend some international contests and obtain the top rankings. For art specialty, get the highest level in the exams.
Develop good skills in one specific art area and in one specific sports area.
Obtain good academic records.
Build good communication and social skills.
Develop good presentation and leadership skills.
Attend various clubs and performances.
Have some community service experiences as volunteers.
Have some part-time working experiences.
Build good relationships with the teachers for letter of recommendation.
It doesn't really matter to choose public school or private school, but it should be the best school reachable by you.