Well, after some serious thinking and pondering and staring long and hard at that calendar, I think I finally cracked the code.
At first I thought it stood for "pumpkin patch" and that I had accidentally written it on the wrong day, but that couldn't be it because the words "pumpkin patch" were already on last Thursday's square. Hmmmm....
But then, I noticed that above the mysterious "p.p.", it said "Aulora - wear messy clothes". Oh yeah! Aulora's class is going to "paint pumpkins"! But why the time 9:30-10:30? That still didn't make sense.
More thinking and eye squinting led me to believe that it must stand for "pumpkin presentation". Julia's teacher is carving a pumpkin in front of all the kids from 9:30-10:30 on Thursday and talking about how it is like Jesus' love for us. They sent home a paper letting us know about it and inviting us to come if we wanted.
What a code cracker I am. Clearly, I'm the next Sherlock Holmes.