We do calendar math every day!
First, we snap or clap as we sing the "Days of the Week" song. When the month changes, we also sing the "Months of the Year" song. Next, we practice reciting the day of the week, month, date, and year for each sentence starter: Today is..., Yesterday was..., Tomorrow will be...
Then, we learn about place value (tens and ones) by adding one straw each school day. We count the straws by twos and recite whether the total is odd or even and how we know. We even learned the "Odd/Even" song (sung to the tune of "BINGO"). The children observe what happens to the straws when we have ten (regrouping). We also use the 120 chart to notice patterns when we add/subtract one and add/subtract ten from the date.
After that, we tally the weather and count the tallies by fives, noting which type of weather has more/less. We also compare the different types of weather--"How many more sunny days than rainy days?" which involves subtraction. Throughout the school year we'll be observing how the weather (and amount of daylight) changes depending on the season (science).
Finally, we add a penny for each school day, recite the name/value of the coins, and count the cents aloud. We also write the total on the board with the cent symbol. When there's enough coins to change for another coin with a higher value, the children take turns explaining to the class how much they have, what coin they want to exchange that amount for, and how they know.