Several of the actors playing the pupils of class 5C were (in some cases, very obviously) in their mid 20's when the series began, despite their characters being meant to be around 15/16.
The pupil's nickname for Mr Hedges is Privet. This is a reference to Privet hedges (usually Ligustrum ovalifolium) which were a popular ornamental privacy hedging used around gardens and property in Britain.
John Alderton, (Mr.Hedges), was only three years older than David Barry who played one of his "teenage" pupils, "Frankie Abbott ".
Gregory Scott who plays Mr Wyatt in S4 E3 was married to Joan Sanderson. Although only credited in the one program, he appeared in many other episodes.