"학생들이 학교에서 고양이를 길러요."
Translation:The students raise a cat at school.
The location describes the verb that comes after it. In Korean, because verbs go at the end the location modifying the verb always comes before the verb.
Btw, 학교에 있는 학생들이 is how you'd say "the students at school". You'll learn about it more in the Modifiers skill but it's important to note that whatever describes the noun comes before the noun.
At school means the person is literally, physically, inside the school. “He's at school. His classes finish at 3:30.” In school means the person is studying in general (usually at college or university) but not necessarily inside the school building at that moment.
English doesn't have the same rules as korean. "The students at school raise cat" should be accepted as in English it has the same meaning as "the students are raising a cat at school." Why would students from a different school raise a cat at this school. It doesn't make sense. So both versions would work.