I enjoy these types of calendars and while I understand that some of the holidays and observances may be made up, I still can use them to promote a skill in my classroom. One of the most successful ways that I have used this idea in my classroom is to write the holiday or observance on the board for children to read as they come to school in the morning. Teachers, faculty, and staff began coming by room to see what the holiday of the day was. They often laughed about it, then left discussing it!
There are activities ideas for each day, often with links, below the printable calendar.