How much actual difference does fixed pitch propeller make in takeoff distance?
With my old VariEze (not a training aircraft; in the same power class as the Cessna 152 but lighter and with much higher wing loading) I had a cruise propeller and a climb propeller that I could exchange on the ground with about 30 mins of work. I measured ground roll at max gross weight and calm wind to be around 1500' with the cruise prop and 1100' with the climb prop. I could usually get around 1500 fpm climb with the climb prop and 1000 fpm with the cruise. Cruise speed was 10 to 15 kts slower with the climb prop depending on altitude; you'd usually have to throttle back quite a lot to avoid exceeding redline RPM.

The difference in takeoff performance is more dramatic when a constant-speed (variable pitch) prop is compared to a fixed-pitch prop. I'm presently in the process of upgrading my Lancair 360 from a cruise/climb compromise fixed-pitch prop to a constant speed and I expect that to decrease the ground roll to less than half the current 1500'. I'll report back with data once it's flying.