Capt M
It is rare to find an SEP POH that gives you the range of hard data to reduce the airspeed relative to the a/c weight, an honourable exception being the SA121 Bulldog.
Following that train of logic through, on what basis could a flight school provide this information to a student? Make it up using a rule of thumb?
You can just imagine what a lawyer would make of such advice where there any problems.