See who can do 100 jumping jacks or run 100 yards the fastest, and provide $100,000 Candy bars as prizes. Or, gather a popcorn popper and 100 unpopped kernels. Ask each student to guess how much space the unpopped kernels will occupy. Then ask them to guess how many of the kernels will pop and how much space the popped corn will occupy. Finally, fill three jars with candy, with one containing exactly 100. Have students guess which jar contains 100 and have them explain how they arrived at their guesses. At the end of the day, give each winner a piece or two of the candy.
Have students toss coins in the air and graph the results: how often does heads come up? Tails? And what is the percentage of each? Or have students list what $100 could buy; ask them to figure in a uniform percentage of sales tax for each item. Also, find the current exchange rate of Euros for American dollars and have students convert 100 pennies, 100 dollars and even 100 million dollars to the Euro.
Line up 100 students and have a group of students measure each one in inches. Ask the classes to convert the total inches to feet as well as half- or quarter-inches. For another activity, ask students to lay 100 pennies side by side and measure them. Then, have them figure out how many times they would have to lay out 100 pennies to travel 100 yards of one mile.
Ask students to write an essay or draw a picture of what school might have been like 100 years ago, or what it will look like in another 100 years. Ask them to draw pictures of what they think they may look like when they are 100 years old. After that, have them do the math to figure out how many days, hours, minutes and seconds make up 100 days or 100 years. If they do the calculations for 100 days, they'll figure out how many days, hours, minutes and seconds they have been in fifth grade.