My son and friends are going to the Expo in early August, and they are students. After reading the official Expo web site, I am still puzzled about ticketing... Too complicated and too many questions not answered. So please someone help me!

1. Can they use student IDs issued by their US high schools to buy Student tickets?
2. Should they buy the tickets in advance?
3. Are the tickets dated? If not, does it mean they can use the tickets any day they choose?

Thanks for answering!