How do you say grammar school in spanish?

There isn't a direct, single translation for "grammar school" in Spanish that covers the exact same meaning as it does in English. The appropriate translation depends on what kind of school you mean:

* If you mean elementary school (ages 5-11 approximately): The most common translation is escuela primaria.

* If you mean middle school (ages 11-14 approximately): This would be escuela secundaria (or sometimes instituto, particularly in some Latin American countries). In some regions, they may use a term that further subdivides secondary education, like secundaria básica.

Therefore, you need to specify the age range or type of school to get the most accurate translation.