"Those schools are here."
Translation:Sekolah-sekolah itu ada di sini.
the most basic indonesian language structure is usually formed of subject+predicate (or at least that's what i learned in school), predicate here can be 'to be' words, verbs, or definition like 'adalah', it gives information about the subject. "sekolah-sekolah itu di sini" is missing the predicate, it can be translated as "those schools here" you are missing 'are', "ada" functions as 'are' signifies location 'to be located' or something like that.
i dont take the indonesian course, so i dont know what they taught you, but in indonesian we sometimes use repetition to mention plural forms, for example rumah-rumah (houses) sekolah-sekolah (schools) bukit-bukit (hills). (there are other forms of plural nouns but that's it for now)