What's the difference between 同学们 and 学生们?

同学们 refers the students or the learners and 学生们 refers the teachers or the person who taught something. In this way, sometimes, students can be 学生们 and teachers can be 同学们。

Generally,“同学们”means classmates,"学生们"means students. 

But“同学们”can also been used by teacher to call the students in a kinder way. 

如果我是一个学生，我可以说：”我的同学在吃饭，或者我的同学们在踢足球。“（同学，是平辈之间的称呼。）

如果我是一个老师，我可以说：“我的学生在吃饭，或者我的学生们在踢足球。”（学生，是老师对学生的称呼。）

但是，按照说话习惯来讲，在上课前，老师会说：“同学们，上课了！（而不是学生们，上课了）我觉得在这里，更加强调整个班里所有的学生。

they are both almost similar, but 同学们 is more kinder compared to 学生们

同学们的使用场景是学生是听话方，说话方一般是老师给学生上课交流时用的。比如，同学们早上好！学生们的使用场景是学生作为被描述的对象，比如学生们在教室里学习

当着学生的面说的话，是同学们。如果和其他人说的话，是学生们，同学们也ok。

“同学们” that people who are student talk or appear sth to their classmate will use it.Also, sometimes the teacher who want to be close to their students will also use it to call the students.It's usually  used  in the conversation of “student - student ”,or “teacher - student ”.

But “学生们” is the name kind of like the people who are the administrators in school talk about the student in the conversation with other teachers.It's usually  used in the conversation between “teacher to teacher”.

同学们是自称，有亲切感，团体感。老师也偶尔会说同学们，有融入和亲近的感觉。相反，学生们就缺乏这种亲切感，只是很客观很冷静的描述一群人。

汉语的一个难点就是字词有褒贬，体现了感情好恶和温度。

Both are plural form of student, but 同 means the same as, together. So when a teacher call the students 同学们, the vocative expression is not just a calling, but also includes concern and kindness, there is equal right between teacher and students.

学生们 is just a plural noun of students, it's neutral. When we use学生们，the teacher is in a higher authorities, lack of humanistic feelings.

So if in the same context, 同学们 is better than学生们。

“同学们”——it  means  classmates

"学生们”——it  means  students