The board of directors of Prairie Meadows Racetrack and Casino yesterday approved an agreement that provides Des Moines and Polk County schools an annual share of gaming revenues. The board unanimously approved an extension of a pact that will pay the schools approximately $4.7 million per year through 2018. The total could rise in future years if Prairie Meadows’ casino revenues go up once its hotel is completed in March. Language in the agreement calls for the terms to be renegotiated if adverse legislation, such as a gaming tax hike or a smoking ban, causes Prairie Meadows’ net revenues to drop. The city of Des Moines and Polk County have already approved the agreement, which will now go before the Iowa Racing and Gaming Commission for approval.