Sibling Rivalry Tip

I have a 3rd grade boy and a 2nd grade girl. They have always gotten along really well, but at the beginning of this school year they started to pick at eachother and constantly fight over who goes first or who gets to sit where in the van. So I decided that on school days, every "odd" calendar date belongs to the first born child and every "even" calendar date belongs to the second born child (for months with the 31st and 1st on back to back school days, the 1st is "mommy's day")

When it is a child's day, he/she gets to decide first where to sit in the van, who will take a bath/shower first, etc. At first, I had to remind my sassy daughter that she is not a Queen for the Day, she just gets to decide things first (because she would boss her brother around and say he had to do things because it's her day!) Now that they have the hang of it, I NEVER say a word- they look at the calendar to see whose day it is, and ask eachother things like, "It's your day- where are you sitting in the van so I know where I can sit?" And at bath time, I just say, "Bathtime! Whose day is it?" and they work it out between them who goes first. Such a beautiful thing!

Oh, by the way, we only do this for school days. Since we do a lot of running around on the weekends, whoever "calls it first" gets to pick first for van seating the first time we go somewhere, then they take turns picking first the rest of the day as we get in and out of the van. For any other issues, they do rock/paper/scissors.

Any other tips for siblings getting along??