It depends upon how fine you make your mesh. If you can make a fine mesh with lots of elements through the thickness, then you should get accurate results. If you've only got one element through the thickness, then your answers are going to be pretty useless. I seem to recall that an old rule of thumb was that two elements through the thickness will at least get you in the ball park. Three elements are better and may give you good enough results if you are not asking for too much accuracy.
It also depends on what your loads and restraints are. If you had a pure tension load, then I would guess that the number of elements through the thickness would be immaterial.