I designed a laser-cut stand for the iPhone 4/4S/5 that holds the phone at the optimal scan height of 9 inches, and leaves space underneath for some kind of workflow (side to side, pile to pile, etc) for when you need to scan a large number of quizzes at once. I made it at TechShop using the Epilog 60-watt Laser Cutter/Engraver and the Formech FLB500 heat strip bender.
Step 1: Laser cut the stand
Step 2: Bend the phone retaining tabs and the main bends of the stand using a strip heater
There are three tabs for retention of the phone and two main bends in the stand. All of these bends are made at 90 degrees with the exception of the main bend nearest the base of the phone. This bend I would make at 95 or 100 degrees, since the 3mm acrylic will tend to bend a little bit with the weight of the iPhone loaded on it. I find when this bend is made at 100 degrees, then the Scan Stand will operate at a 90 degree bend with the weight of the iPhone 4S loaded on it. If available, use a folding jig with protractor to make sure your angles are correct.