"L'année prochaine, tu vas découvrir le collège."
Translation:Next year, you are going to get to know middle school.
Four grades or forms, ages 11-15. Puberty school. And the teachers are called les professeurs.
Some English educational authorities have a 3 tier system, loosely Nursery to Year 4 (infant) year 5 to year 8 (middle) and year 9 to year 13 (high). This can also be found in the private school (confusingly for foreigners also known as the 'public school') system. Sorry but I do not know how it works in the French system.