ANSWER: I would recommend setting up something on your monthly treasurer's report to show the Scholastic credit as if it were a designated fund, showing the initial amount of the credit, the amount "spent" to date and the balance. In addition you should add a recurring footnote indicating amount of credit given, amount spent, amount remaining, the expiration date and the plan you have in place for spending the credits, for example, "The PTA will donate 150 credits to the school library each school year from 2013-14 to 2015-16."
On the final footnoted report you would indicate that the credit has been used fully and there will no longer be a footnote attached to the financials. If it carries from one budget cycle to the next, you would want to add a footnote to the new budget indicating the remainder of the credit to be spent again noting the beginning credit, amount spent in previous year and the amount remaining.
By keeping this information on your treasurer’s report, it will help to make sure that this account is not forgotten as volunteer leaders transition in and out as well as be a true accounting of your PTA’s assets.