Formal:
* L'assemblée générale: This is the most literal translation and is often used for official school assemblies.
* La réunion scolaire: This is a more general term for a school meeting, and can also be used for assemblies.
Informal:
* L'assemblée: This is a shortened version of "l'assemblée générale" and is more commonly used in informal settings.
* La réunion: Similar to "la réunion scolaire", but without the specific reference to school.
Other options:
* La cérémonie: This can be used for special assemblies, like graduation ceremonies.
* La rencontre: This can be used for assemblies that focus on a specific topic or theme.
Ultimately, the best way to say "school assembly" in French depends on the specific context and the level of formality you want to achieve.