After Mrs Norris and Colin Creevey are attacked, Ernie is highly suspicious of Harry because he is a Parselmouth. Harry overhears Ernie telling a group of other Hufflepuffs that he believes Harry is the heir of Slytherin and when Justin Finch-Fletchley is found Petrified, Ernie is quick to accuse Harry. However, after Hermione is attacked, Ernie apologises to Harry, saying that he knows Harry would never have hurt her. Ernie and Hannah Abbott join Harry and Ron in Herbology, and Ernie wonders aloud whether Draco Malfoy might be the heir.
Ernie attends the Quidditch World Cup during the summer holidays. He is staying at the same campsite as Harry, Hermione and the Weasleys. He greets Harry, Ron and Hermione as they walk through the campsite on their way back from the water tap.
Ernie attends the Apparition lesson in the Great Hall. He takes the Apparition Instructor seriously, focusing on his determination, contemplating his hoop so hard his face turns pink, looking as though he is trying to lay a Quaffle-sized egg. On his first attempt, Ernie does a pirouetting leap into his hoop, looking momentarily thrilled as he believes he has successfully Apparated.