It's not just "another" school day, it's First Communion Day. The school the girls attend to have the policy of gala uniform (blazer and tie are compulsory) for all students at their local church in Aravaca. Leonor attended the communion as a guest, not a student, and was able to wear whatever formal clothes she wanted. In Spain is very rare, and extremely difficult, to celebrate a first communion on your own. The majority do it with classmates (accepting the school polity attire) or with their Sunday school classmates.
First communions have gone so much out of hand that they rival weddings in expenditure. People spend thousands in between the dress, the hairdresser, jewelry, restaurant's menu ....As the following article states what used to be a celebration of tea and cakes, today is a masterchef lunch, a trip to Eurodisney and the latest mobile phone.
One paragraph of the article reflects the current situation better than most ....."As we go, the banks will have to grant micro-credits so that we can live up to the gifts and dinners that are currently organized to celebrate first communions"
It's no wonder that there is growing backlash from many schools wanting to make communions a more simple and humble affair focused on the rites and not the "social party".
http://verne.elpais.com/verne/2017/05/16/articulo/1494942038_307879.html