Continuity mistake: In the scene when Bob takes Ritchie to "get laid", Bob approaches the girl in the pink dress at the end of the row, while Ritchie goes to play La Bamba. You see Ritchie play La Bamba and in the background Bob is all over that girl. The next shot cuts to Bob just arriving at the girl.
Continuity mistake: When Ritchie's brother lies down next to him in his bed, the covers are down to Ritchie's stomach whenever they show him in a solo shot, but are pulled up almost to his neck when the shot shows both brothers together. In the next solo shot of Ritchie, the covers are back near his stomach again.
Continuity mistake: When Richie and his brother Bob get into a fight, Bob pulls on Richie's sweater and yanks his tie out of kilter. A few seconds later, Richie's tie is tucked in and his sweater is smoothed down, but not enough time has elapsed for him to have done this to himself. (01:00:34)