Continuity mistake: After the kindergarten class have finished their speech, the little kid who spoke last turns around and begins to jump up and down. When the shot changes as the principal starts to speak, he is facing the front, standing perfectly still.
Other mistake: When Det. Kimble comes out of the school on the stretcher, we see all his class gathered by his side yet still next to the school. Standard FEMA operating procedures (and common sense) would have had the kids far away from the school and not standing near the entrance emergency workers are actively using to get the fire under control.
Continuity mistake: Toward the end of the film while the school is on fire, Kimble's partner runs to the side door, gun drawn. Phoebe is spotted by Crisp's mom and is hit by her car, knocking her down. Crisps mom's hair is pulled back, but when she is in the school locker room and discovers Crisp shot dead her hair style is different, not pulled back.
Continuity mistake: Earlier in the movie... when Kimble is looking for Cindy (just before the "line-up") and Arnold says the line - "Alright party's over, everyone go home" he tosses some guy onto the glass coffee table which gets completely destroyed. Arnold's next line a moment later is, "next time, my place." The next scene, the coffee table appears good as new and the the guy is no longer there.
Revealing mistake: In the shot where Dominic is falling from the radio tower from afar, he supposedly gets hung up by his backpack. However the lack of tension on the straps indicate that something else kept him from falling. We see the proper tension on the backpack when the scenes change to an up close shot.