How to teach probability

Grade 3 to Grade 6

Probability measures how likely an event is, from impossible to certain. Students first describe chance in words (impossible, unlikely, even chance, likely, certain), then put it on a 0 to 1 scale, and finally write simple probabilities as fractions: favourable outcomes over the total number of equally likely outcomes.

How to teach it

1. Start with everyday language and order the words on a line from impossible (0) to certain (1), with even chance in the middle.
2. Use fair, equally likely situations first: a coin, a dice, a spinner with equal sections.
3. Count outcomes: the probability of an event is the number of favourable outcomes over the total number of equally likely outcomes.
4. Show a probability is a fraction from 0 to 1, and that all the outcomes' probabilities add to 1.
5. Compare theory with experiment: predict, then roll or spin many times and watch the results settle near the prediction.

Worked example

Chance of rolling a 4 on a fair dice:

   favourable outcomes: 1 (just the 4)
   total outcomes: 6
   probability = 1/6

Common mistakes

• Thinking every event is 50/50 because there are two results (rain or no rain is not even).
• Counting outcomes that are not equally likely as if they were.
• Writing a probability bigger than 1, or as a whole number.
• Believing a run of heads makes tails 'due' on the next fair toss.