I feel that I have to put in my experience into this thread. Myself are flying full scale and have flown types that do pitch down as well as types that are pitching up when applying flaps.

First of I would like to say that I agree with many of the inputs on this thread regarding this issue.

Basically a high wing aircraft will pitch down and a low wing will pitch up when extending flaps. Opposit will happen when retracting. As the pilot changing the airfoil shape, by extending or retracting flaps, there will be a new point of pressure along the cordline. Thus the distance towards the center of gravity changes. This will call for triming the aircraft in order to maintain level flight. Obviosly, if extending flaps, wich means getting more drag, also more thrust/power is needed to maintain current airspeed.
However, there is no universal rule to high and low wing versus pitch up and pitching down, since every airfoil and aircraft has its own carateristics. It is basically up to the designer of the a/c to put into the design what he/she is looking for. But after been flying 14 different types the past 8 yrs, including high and low wing aircraft with piston turboprop and jet engines being singels and twins, it "usally" turns out that high wing aircraft are pitching down when extending flaps and low wing does the opposit.

Christian