I noticed the same phenomenon as you with both my sons—teachers doing basically the same calendar routine in preschool, kindergarten, first grade, and second. This occurs because preschool and kindergarten teachers co-opt the elementary school curriculum and twist, pound, and mold it to use with their young students. Taking lessons that are designed for older kids and thrusting them upon those who aren't ready is not only a waste of precious time in preschool, but is potentially harmful and definitely outside the realm of what's considered developmentally appropriate. Too many parents get easily impressed by calendar activities in preschool (thinking their kids are getting “advanced” instruction) when, in reality, time could be much better spent on playing, exploring, and interacting.
Decades of research shows that little children learn differently than older ones, and that's why we have the field of early childhood education. Their brains are wired for sensory experiences, hands-on exploration, and kinesthetic learning. Sitting at circle time as the teacher drones on about numerals and patterns on the calendar is no benefit to them. Trying to make sense of time concepts such as yesterday, today, and tomorrow causes them unnecessary confusion, stress, and frustration.
I recently visited a top-notch preschool where an astute teacher did an amazing thing. After years of dutifully doing the calendar every morning with her class, she looked at the little faces before her and saw zombies. She had always loved doing the calendar (in fact, it was her favorite part of being a preschool teacher) but at that moment she saw how boring it was for the kids. After school that day she took down her gigantic calendar and gathered up all her calendar supplies.
The next week when her students came to school there was, much to their delight, a new dramatic play area in the corner—a classroom! It included a desk, chairs, writing materials, a chalkboard and, yes, that enormous calendar and all the calendar supplies. From that day forward, the children would pretend to be teachers. Instead of watching her go through the days of the week, the numerals, and the patterns, they got to do it by interacting with the materials themselves, not just sitting there and watching. It was preschool education at its very best!