2) When you are calculating the costs per student for the purpose of valuing vouchers, I'd guess you need to include the students who are are being homeschooled or are currently attending private schools without vouchers as part of the denominator. Presumably the vouchers wouldn't be restricted to only the students who are switching, but instead would be given to all? Since about 10% of students are currently private schooled (I presume homeschooling is much lower?), this would reduce the "fair" value of the voucher by another 10% or so if you were trying to keep it cost neutral.