Is there a word or a phrase for "a student who sits at the back of the classroom"?
I came across the word "backbencher" in some text but it was written by non-native speakers of English.
I'd like to know what native speakers think.
You can use the term back-row students to describe the students that you talk about. Wiktionary has a usage note which says:
The back row of a classroom is associated with delinquent behavior by students wishing to avoid the teacher's attention.
One example of this term being used in this way is from a blog post by a dean of students:
The under-engaged student is perhaps the most elusive types of students you will encounter during your teaching career. When they come to class, they are usually late, sit in the back row, put their headphones in, and their head down. In an online class, they tend to vanish suddenly and quietly, reemerging to take an exam or submit an assignment. These “back row” students present some interesting challenges, but also some of the most rewarding teaching experiences.
Another blogger used this term to describe his own educational experience:
I was a back-row student, surrounded by like-minded souls, snapping gum, sneaking out the back for cigarettes.
It's important to note: not all students who sit in the back row are necessarily "back-row students", and assuming that's the case would be unfair stereotyping. Although the term can refer to students who are more interested in checking their Facebook page than listening to their instructor, sometimes the reference isn't so negative. For example, a book about online learning talks more about shyness than delinquency:
The online learning environment removes the social pressure and anxiety from classroom interactions. On the online discussion board, it is almost impossible to distinguish the shy “back row” students from the talkative “front row” students.
Since students voluntarily choose their seating location on the first day of the course, this may indicate that back-row students begin the semester with a lack of initiative to interact or with a generalized lack of confidence in their abilities.