"Algunos estudiantes en la clase son bajos."
Translation:Some students in the class are short.
It would appear that because I wrote, "Some of the students" instead of "some students" the system rejected with the message, "Some of the students in the class are small."
Yes, DL tries to 'modify' your answer to the closest acceptable version. If you then make some other 'fault' that DL-machine hasn't got a correct answer, it might even give you 'abla-babla' -faulty suggestion. That is; the best in line that it has. Or you get a warning : "you used a/the wrong word". In order to continue you just have to accept the sentence DL gives you no matter what. But then you get also a possibility to remind: press the red flag, and you can report the thing (but it isn't really a proper feedback, though)
Duolingo said that this is incorrect. "a few of the students in the class are short". Reported!