A Comedy On This Day: Please Sir! - What Are You Incinerating? (1 January 1972)

 I've never seen any of the final series before. The original Fenn Street Gang Class 5C might have been incongruously superannuated, but their 4C replacements were an undistinguished bunch. Bernard Holley's teacher is certainly not as distinctive a character as Hedges was... The most problematic substitution is Geoff Rowley & Andy Baker for Esmonde & Larbey, though - a lot of unconvincing caper stuff with an escaped mouse and an explosion, but nothing much about being a schoolteacher anymore.