Since 1985 Radio 4's King Street Junior has become a radio classic. Its author, Jim Eldridge, has fitered life among Junior School teahcers to produce a genuine essence. It feels real because in many ways it is. Each wave of change in state education - curriculum reform, parental governors, strikes, budget cuts - has ripped into King Street Junior. The proramme gets fan mail from teachers, all of whom believe it must have been based on their schools. If that is the situation, the comedy is bred deeper, good writing so well performed that it creates another world.