I assumed that "pre-school" meant that it was marketed to families with children who are preschool age. They are the least likely to have difficulty planning vacations for late-August thru September because they would be less concerned about working around a chool schedule.
Thanks for the info- I thought it couldn't be that clear! I'm still sleep deprived from our newest little one- our school system has just gone to extended school year so they adopted 2 days off for labor day break next fall- that coupled with the free dining sent me into planning mode!
Actually YWM is the "preschool" code. It was published in Parents Magazine. The two codes give you exactly the same offer. Disney just created separate marketing codes in order to track where the business was coming from.