How did Scrooge pass time when he was alone at school for Christmas?

Scrooge passed the time by reading.

They went, the Ghost and Scrooge, across the hall, to a door at the back of the house. It opened before them, and disclosed a long, bare, melancholy room, made barer still by lines of plain deal forms and desks. At one of these a lonely boy was reading near a feeble fire; and Scrooge sat down upon a form, and wept to see his poor forgotten self as he used to be.