Students are divided into four houses at Hogwarts. The Houses are named after the four wizards that founded the school Godfrey Gryffindor, Helga Hufflepuff, Rowena Ravenclaw and Salazar Slytherin. The decision on what house an individual will be assigned to is determined by the Sorting Hat.
Ravenclaw
Ravenclaw Class Listings
Hufflepuff
Hufflepuff Class Listings
Slytherin
Slytherin Class Listings
Gryffindor
Gryffindor Class Listings
The following students don't have a specific house identified 
  MacDougal, Morag (Class of 1999) 
  Moon 
  Nott 
  Parkinson 
  Perks, Sally-Anne 
  Macmillan
  Miss Fawcett