Why does Pap disapprove Huck?

Pap harasses Huck for wearing good clothes and going to school. He then accuses Huck of putting on airs and acting better than his own father. Pap remarks that no one in his family could ever read, and that he certainly does not want his son to be smarter than he is. He demands that Huck read him something, and soon becomes quite furious when he realizes that Huck is in fact able to read. Pap threatens to beat Huck if he ever catches him near the school again. He makes Huck hand over the dollar that Judge Thatcher "paid" him and then climbs out the window to go drinking in the town.