Continuity mistake: When Mike takes the family photo he's smiling, but in the next shot with the photo printed he's not.
Continuity mistake: In the scene where Avery and Kayla confront Lina at her locker, as the shots change, so does Lina's position. She goes from leaning against the locker, to standing close it. Her arms are also crossed/uncrossed as the shots change.
Continuity mistake: In the football match between the Millwall gang and the West Ham gang, the team names switch places on the scoreboard between shots. You can also see the score points switch places throughout the scene behind the Governor and Arthur. (01:16:05)