Birthdays allow students to personalize statistical probability. Ask the class if it is anyone's birthday today. Whether it is or isn't, have the class calculate the probability of someone having a birthday today. The way to calculate the probability is to divide the number of students by days in the year. However, let students figure this out for themselves. Once they have done this, ask them the probability of two students having a birthday on the same day. This exercise serves as a useful introduction to calculating probability.
Statistical probability does not always play out in the real world. Illustrate this problem with the game of Pig. Break the class into groups of three of four. Give each group a die. Players take turns rolling. Students collect the number of points that the die shows on each roll. However, if they roll a one, they lose all their points. Students can stop anytime and keep their points. Students will learn that although they have a one-in-six chance of rolling a one, they might go on a long streak without losing their points.
Bring some small toy cars into the classroom. Set up a sheet of paper on the ground with at least 12 spaces, placing two cars in the first space. Have two students race each other. They take turns rolling a die, moving their car up as many spaces as they roll. The student who is ahead after a predefined equal number of rolls wins the game. Allow the winner to stay on until he is defeated. Have students discuss the probability of one student staying on for a number of turns.
There are a variety of online probability games for kids. One of the best is a simple game at Kids Math Games. Players are presented with a lottery machine featuring a variety of colored balls. Players must decide - on a scale of certain to impossible - how likely each color is to come up. Players can then activate the lottery machine to see what happens. The cartoon-like graphics and sounds are certain to appeal to fourth-graders.