"I am a university student and my brother is a pupil."
Translation:Ich bin Student und mein Bruder ist Schüler.
Any Student is never a University Student. Which is why the word "University" (Universität Student) is used to differentiate that. Student, in general is for all levels but a University Student (Universität Student) is actually of higher level (niveau) See Edu. Chart. The highest level in University. All other levels are just Students. https://goo.gl/images/BAo9G7
see discussion here: https://forum.duolingo.com/comment/2333/Student-vs-Sch%C3%BCler