For a high school kid, I think it's generally accepted that a 90 minute run or so is a good distance for a long run. My question is what does the long run do for you? Personally, I think it sure does something, because once I started running ~13 miles every Sunday, I saw HUGE improvements in my times.
Now, not totally sure if this is true or not, but I think that the long run indirectly helps me with my times in the 800-5k. It's almost as if when I do them regularly, my other training runs are inhanced, thus running faster times. Yea, this is semi-troll, but I'm trying to be kind of sincere. What do you guys think?