Epple and Romano (2008) describe theoretical evidence that school vouchers will lead to "cream skimming," where private schools will pick off the better students and leave public schools with lower-ability average students. They propose targeted vouchers, in which different-sized vouchers go to different groups of students, to combat this potential concern. Suppose you are asked to design a targeted voucher system to reduce the level of cream-skimming. You decide to vary the value of voucher for different students. Which students would get larger dollar-value vouchers, and which could get smaller dollar-value vouchers in your system? explain briefly