After an impressive couple of episodes this was rather a return to the fairly lacklustre standard of the early outings of Series 4. It still has its moments but is very much in the shadow of the first three series.
After his arrival in episode 5 David Ffitchett-Brown in trying to freshen things up further by getting some new teaching aids including a new television and posters. Maybe this might address another problem of a couple of pupils who have been truanting and perhaps feel school has little to enthuse them. He finds them at the local billiards (snooker) hall and tries to get them back to Fenn Street.
The core difficulty of Series 4 so far is illustrated here - the pupils have rather gone missing from the action and the focus has become too much on the staff. The staff interactions are still entertaining but the strength of the earlier series was that there was a core of memorable pupils who could engage in their own right as well as through their scenes with the teachers. Pupils have been featured in Series 4 but with no consistent focus so they become rather anonymous, Their characters also largely lack comedic value and in this story the focus on student disaffection is perhaps too close to realism than suits a sitcom. It's interesting to see early appearances by Robin Asquith and Shirley Cheriton (later of Eastenders) but little else from them to command interest. Shirley Cheriton is though unusual in being a Fenn Street pupil who does look in her mid-teens rather than her mid-twenties!
The focus on "billiards" (the pupils are actually playing snooker but the game was less well-known then) is interesting. Most of the staff - most notably the Head - see billiard halls as places of bad influence, a stereotype / cliche that was quite common then. A few years later the game became very popular thanks to TV exposure and it lost that dubious reputation.
As usual Potter messes things up to the frustration of all the staff except the indulgent Head. There is a striking sequence in which they are criticising him and fail to notice that he has entered the staffroom and can hear their harsh (though accurate) words. How would Potter deal with this denunciation? "Please Sir!" was changing a lot but Potter's incompetence was a constant source of frustration for his colleagues - and humour for his viewers.