***** NOT A TEACHER *****
Hello, Mr. Mangalore:
I believe that sentence could be changed to:
"Although she was ill, the student attended classes."
"Although she was ill" is a subordinate clause because it depends on the main clause ("The student attended classes") to make sense.
P.S. Your sentence did not specify the gender of the student. In 2014, when we do not know the gender of a person, we can refer to that person by either the male or female pronoun. I decided to use "she."
Compare: Although Raul was ill, he attended classes. / Although Maria was ill, she attended classes. / Although he was ill, Raul attended classes. / Although she was ill, Maria attended classes.
P.P.S. We can say "in spite of" or "despite."
Interested in Language