Spread the word before school lets out for summer: the high school that sends the most students throughout the season to hear the Chicago Symphony Orchestra at Ravinia Festival will receive a cash donation for its music programs in the fall. Best of all, lawn admission is free to all these students. They simply need to show ID at the box office, so points can be recorded for their school(s). To make things fair, the points will be weighted on a map of concentric circles, so the students who travel furthest will get more points than students who live closer. All students will win double points when they attend the second annual “Cannon Ball,” a hang-out with free food and refreshments prior to the July 29 all-Tchaikovsky concert. That concert will feature live cannon explosions in the “1812” overture. For information, register at the facebook page.