When you read the phrase, "the first day of school," does it give you an emotional reaction? It does me. Today was my kids' first day back at school, and between excitement and jetlag they both woke up about 4:30am. I know lots of moms who are sentimental about the departure of their last-born to kindergarten, but I was more excited for her than sad. It's different if you've had the baby at home the entire time... but my girl wanted to go to preschool with her brother from age 2, so I guess I'm used to it. I also love the idea of more time for my writing!
If you're like me, and you are thinking about worldbuilding, there's an incredible richness of opportunity in something as simple as a day like this. Many societies have big transition points built into them, though they differ across cultures and within cultures as well. Here's a real life example: because I grew up with a professor and a school teacher as parents, our entire life schedule revolved around the school year and summer vacations - and it took some time for me to adapt to living with my husband, who works the 9-5 job all year round.
I always find a story more exciting and real if I can share the emotional reactions of the characters to what is going on around them. Think about the emotional reaction you get just to the phrase "first day of school" - and then think about what you might do with that. You could create a society where the first day of school means something totally different - maybe something scary and horrible instead of scary and exciting. If school is something where you don't see your parents at all, that changes things too. Take a pre-existing emotional reaction and tweak it - send it in a different direction. Or take a pre-existing event, and change it, but keep the emotional response the same. On an alien or fantasy world, what kind of life-changing day would there be to inspire "first day of school" feelings in its inhabitants?
It's something worth thinking about... and now I have to go pick up my daughter!