I wouldn't be encouraging students to set a specific ROD in the cct. On base leg I give them a 'starter for ten' power setting which in a 152/172/PA28 would be in the region of 1600-1700 rpm, set two stages of flap and maintain level flight attitude until approach speed + 5 is met. Only then should they set an attitude to maintain that speed, trimming as necessary. From now on they should be judging their ROD from the runway 'picture', airspeed from the horizon and rarely look inside the cockpit.
Taking a step back, I'm rather wary of being so prescriptive as far as visual ccts are concerned.