To add to what Rotaryphile (what does a rotaryphile know about airplanes anyway :-) said - and to disagree with what adam_one said - if you take wind tunnel data on rolling moment due to aileron deflection, Clda, it is constant over a fairly large range of angles of attack and 0 to 20 degrees of aileron deflections. Only when the wing is partially or totally separated does the effectivness go down. There isn't a boundary layer effect at any practical flying speeds.