A rectangular wing with a constant airfoil section, accurately built will stall from the root outward, and shouldn’t need any wing washout. (but like BMatthews said, It won’t do any particular harm in a trainer.) However, understand that if wing stalls symmetrically, even if it stalls at the tips first, It won’t drop a wing, it will merely pitch forward. The problem comes when a wing stalls concurrent with yaw. In that case one side stalls while the other is still lifting and it rolls toward the stalled side. If the wing tends to stall from the center outward, this rolling moment is rather mild, but if it stalls first at the tips, the roll can be sudden and violent. The fact remains that the yaw is the basic cause of the typical “tip stall” incident.

The ultimate solution is to eliminate the yawing moment. Use of the rudder whenever the ailerons are deflected will help. Differential aileron motion will help although it is a little more effort to install. Coupling the rudder with the ailerons either mechanically or with mixing will help. All of these have been used on full scale aircraft with some success. If the student wants to advance to more aerobatic aircraft, the use of rudder is the only real solution. An airplane designed to reduce effects of tip stall will be difficult to snap roll. And washout becomes washin in inverted flight which makes the problem worse.