They have the same meaning, but it depends on whom you talk with. 他们的意思是一样的（除了单数和复数不一样），但取决于你说话的对象。 If you talk with a group of students, you should call them "同学们", but you cannot call them "学生/学生们". 如果你对着一群学生讲话，你要称呼他们（对方）“同学们”，但你不能称呼他们“学生/学生们”。 If you talk about a group of students with your friend, you should tell him " （那些）学生们/（那些）学生/（那些）同学", but you can't say"（那些）同学们" 如果你跟你的朋友讨论一群学生，你要跟他说“（那些）学生们（复数）/（那些）学生（单数）/（那些）同学（单数）”，而不能说“（那些）同学们（复数）”。

1 In Chinese actually we don't have a very accurate concept about singular and plural like English, eg 这些是我的学生 (These are my students) 他是我的学生 (He is my student) But you could also say 这些是我的学生们 it's no problem. 2 A simple way to tell these two words is that 同学 >> classmate, 学生 >> student However few situation in Chinese are steady, unchangeable. Pretend that a teacher is talking to his students 'hi everyone, good morning' so in Chinese it's probably >> 嗨大家好/ 嗨同学们，早上好 Although the kids are his students, he won't say 学生 but 同学 in this context. About sir Benjamin's answer, >> If you talk about a group of students with your friend, you should tell him " （那些）学生们/（那些）学生/（那些）同学", but you can't say"（那些）同学们" << I don't understand, if you think 那些同学 here is appropriate, why not 那些同学们? It's contradictory, I would say I guess only 那些学生 or 那些学生们 sound more natural into the context sir Benjamin sets.

学生----Students classmate in chinese means some student in one same class ,so these students they are classmate

student 是“学生”的意思 fellow students 才是“同学” 但是将students放在课堂用语的语境中也可以用作“同学们”

students是学生 classmates是同学