Is it customary in Poland for students to give the teacher a gift at the end of the term?
It's costumary to give flowers to a teacher who is "wychowawca" (tutor?) of a class. Also it is costumary to give flowers to wychowawca in Dzień Edukacji Narodowej (14th of October) which is called colloquially Day of a Teacher (Dzień Nauczyciela).
It is costumary only in elementary, middle and high school. Absolutely not in Universities. Although its costumary to give flowers after presentation of your thesis.
I never did such a thing, although I was close to a few and I gave them gift when my university was over. But its kinda strange to give gifts to a person who might be responsible for your grade
where have you lived? certainly not in Poland.
It is a custom and EVERY child gives flowers to his/her class tutor.
Of course it is not a bribe or anything like that. Just a standard way of showing a respect for a proffesion of teacher.