He took a run up from outside the classroom, in the corridor, and gave a hell of a whack. I was at Pontypridd Grammar too so remember him well. He was a nice bloke apart from the the blatant sadism. And as you you say a Geometry teacher too. A fair few of the teachers there knew how to punish kids. Canes across the back of the legs, back of the hands, palm of the hands and one guy across the face. And we had to avoid board dusters been launched at us.