Lycée vs. école secondaire

The French educational system has distinct terms for various stages of schooling. Understanding the difference between 'lycée' and 'école secondaire' is key to comprehending the structure of French secondary education.

Lycée

A type of secondary school in France, typically referring to the last three years of secondary education, encompassing grades 10 through 12 (seconde, première, terminale). It prepares students for the baccalauréat (baccalaureate), which is required for entrance into university.
Après avoir obtenu son diplôme du collège, il est allé au lycée pour continuer ses études.
(After graduating from middle school, he went to high school to continue his studies.)
Elle est professeure de mathématiques dans un lycée.
(She is a mathematics teacher at a high school.)
Les élèves de lycée se préparent pour le baccalauréat en fin d'année.
(High school students are preparing for the baccalaureate at the end of the year.)

École secondaire

A general term for secondary schools in French-speaking countries, it may refer to any institution providing education between primary school and higher education, often including both 'collège' (middle school) and 'lycée' (high school). The term is broader and not as specific as 'lycée'.
En Belgique, l'école secondaire commence à 12 ans et se termine à 18 ans.
(In Belgium, secondary school starts at 12 years old and ends at 18 years old.)
Mon fils est en cinquième année d'école secondaire, qui correspond au collège en France.
(My son is in the fifth year of secondary school, which corresponds to middle school in France.)
La réforme de l'éducation a changé la structure de l'école secondaire dans notre région.
(The education reform changed the structure of secondary school in our region.)

Summary

To summarize, 'lycée' specifically refers to the latter part of secondary education in France—essentially high school—while 'école secondaire' is a broader term that can encompass all secondary education levels including both middle and high school. The term 'école secondaire' may also be used more generally in other French-speaking regions outside of France but can vary based on the country's specific educational system structure.