The C152 POH says that any normal takeoff should be with carb heat COLD, and as part of the BEFORE LANDING checklist it should be set ON. It doesn't make mention of if it should be set to COLD on short final!
The C152 POH (mine is April 1981) states before landing carb heat on (apply full heat before reducing power). For baulked landing the POH states throttle full open then carb heat to cold. However the aircraft is doing a take-off (touch and go) which is just a fancy baulked landing and the POH states carb heat should be cold. Therefore to ensure full power is available for the take off your instructor was wrong to leave the carb heat on during the take off run and subsequent climb to his personal choice of 300 ft In any case where did he dream up 300 ft as the height to place the carb heat back to off?
As another example of instructor personal ideas confounding common sense, I was undergoing a dual check in a Navajo. The instructor insisted the cowl flaps should be set to fully open on final in case (in his own words) we had to go-around. The fact that it would take us only 45 seconds to get back to circuit height went over his head and the CHT was never going to be a problem in that time.