Monkeyman! / Buses, Bikes and Subways - S5-E1
Revealing mistake: Mr. Simmons counts 30 students in the bus, but nowhere near that many got off (nor have nearly that many fourth graders ever been shown).
Stuck in a Tree / Rhonda Goes Broke - S5-E10
Revealing mistake: In the scene after the garbage dumpster scene, Buckley's lips disappear briefly while he's talking.
Revealing mistake: Phoebe is going into the school in one scene, but as the camera moves she vanishes while on screen.
Answer: The show is based in present day times. Plus most cars aren't old fashtioned, I recall seeing a limo and not to mention a cherry picker, etc.