Single word for lazy student
Slacker — Dictionary.com
a person who evades his or her duty or work
Good-for-nothing — TFD
A person of little worth or usefulness.
Couch potato — TFD
an idler who spends much time on a couch (usually watching television)
Couldn't find any word specifically tailored for students. Aren't most students like this anyway?
I think slacker works the best here:
a person who avoids work or effort
[Google]