Michelle, I have the excellent *The Art of French Pastry* by Jacquy Pfeiffer which
has 2 pages of explanation on how to bake the perfect crust. One key step (with added illustrations to indicate his point) is there must not be any gap between the base of the pan and the side of the pan. Think of the dough as making a perfect 90 degree angle. If there is any curve in the dough between side and base (picture an air gap), then the dough will slide down during baking. As important is NOT to press the dough into the seam or it thins out.
Instead, ease the dough into the pan and put just enough pressure on it be sure there is no gap. You should see a line where the side meets the bottom.
More hints:
If using a cutting board, refrigerate board for 30 minutes before. Do NOT use it if it is warped at all.
Dough must be perfectly even. He uses bars the thickness of the finished dough and rotates them top/bottom and then side/side to ensure even thickness.
VERY LIGHTLY butter pans with softened butter. Do not use oil or pan spray. If you can "see" the butter, you have used too much and the dough will slide down the side of the pan when baked.
Side note: The author has the official "certificat d'aptitude professionelle" and one of his course test was this: The student rolls out the dough and lines the tart pan, getting it ready to bake. But before they can do this, the judge grabs the unbaked tart ring and rolls it on its side down an 8-foot table. If the dough in the pan is not properly lined, it will collapse inward.
His tart pan passed the test and he passed the course with highest honors.