"They enter those schools."

Translation: Mereka masuk ke sekolah-sekolah itu.

[Lisa-Lisa-Lisa]

why would you need " ke"?
why not mereka masuk sekolah sekolah itu

[AbdullahAAK]

it's now accepted

[Elvin284427]

why can't i use "mereka masuk masuk sekolah itu?"

[Rick392366]

why can't i use "mereka masuk masuk sekolah itu?"

The EN sentence mentions 'schools' in plural form.
The ID sentence should be 'sekolah-sekolah' to indicate the plural form.
No need to reduplicate 'masuk'.