ACARA v9 CONTENT DESCRIPTION “describe possible everyday events and order their chances of occurring, using the language of chance, and conduct repeated chance experiments to observe and describe variation in results”
Year 3 gave chance its words — certain, likely, unlikely, impossible. Year 4 takes two steps further: first ordering events along the chance scale, and then testing chance by experiment. Ordering means more than labelling: given several events, a child places them in sequence from least to most likely, adding an even chance in the middle where an outcome is just as likely to happen as not. This finer scale lets children compare events rather than only label them, and it sets up the second idea of the unit, that chance can be observed by actually doing an experiment many times.
Order it on the scale
Chance runs from impossible to certain. Place each event where it belongs.
Where does this event sit on the chance scale: "The sun rises tomorrow"?
A finer chance scale
The chance scale gains a useful middle point in Year 4: the even chance, where something is just as likely to happen as not, like a tossed coin landing heads. Now events can be ordered across five positions — impossible, unlikely, even chance, likely, certain — and any everyday event finds a place. The sun rising is certain; rolling a seven on a die is impossible; rain next month is likely; a single six is unlikely. Placing events in order, not just naming each, is the comparing skill that makes chance language genuinely useful for describing the world.
Spin the spinner
A chance experiment is a single trial with an uncertain result. Spin and see.
Four equal colours, one pointer. Each spin is a trial, and you cannot know the result before it happens.
Chance you can test
The big new idea is that chance is not only described in words; it can be tested by experiment. A chance experiment is a single trial with an uncertain result — one spin of a spinner, one toss of a coin, one roll of a die. Before the trial, the result is unknown, which is exactly what makes it a chance event. A spinner with four equal colours gives each colour the same chance on any one spin, and doing the spin turns an abstract chance into a concrete result. This is the move from talking about chance to investigating it.
Tally the spins
Repeating a chance experiment many times means recording each result with a tally.
Record each spin with a tally in its colour. Repeating the trial builds up the results.
Repeating the experiment
One trial tells you little; the power comes from repeating. Conducting a chance experiment many times and tallying each result, in its category, is how chance is studied properly. The tally from Statistics does the recording, and after many spins a pattern of results builds up. Repeating matters because a single spin could land on anything, but many spins together reveal how the chances actually play out. This habit of running many trials and recording them carefully is the heart of experimental probability at Year 4.
More spins, closer
A few trials can stray far from expected; many trials settle near it.
7 of 10 is 70% — with few trials, results can sit well away from half.
More trials, closer to expected
A striking thing happens as the number of trials grows: the share of each result settles toward what chance predicts. Toss a fair coin ten times and you might get seven heads, far from half; toss it two hundred times and the share of heads sits close to half. With few trials the results can stray a long way from expected, but with many they close in. This does not mean the coin remembers or corrects itself — each toss is independent — only that more trials average out the bumps. Seeing results approach the expected share is one of the most important ideas in all of probability.
Predict, then spin
The chance of one trial predicts roughly what many trials will give.
Before spinning, predict the result over many trials from the chance of one trial.
Predicting many trials
Because results settle toward expected over many trials, the chance of one trial lets a child predict roughly what many will give. A fair coin tossed twenty times should give about ten heads; a four-colour spinner spun twenty times should land on blue about five times; a die rolled sixty times should show about ten sixes. The prediction is found by giving each outcome its fair share of the trials. Real results will vary around the prediction rather than match it exactly, but a good prediction sets the expectation, and comparing it to what actually happens is what an experiment is for.
Same test, different results
Repeating an identical experiment gives results that vary around the expected value.
The same coin, the same 10 tosses, run four times. Reveal each run and watch the results differ.
Variation is what chance looks like
Run the very same experiment again and the results will differ — ten tosses might give six heads one time, four the next, seven the time after. This difference between identical experiments is called variation, and it is not a mistake or a flaw: it is exactly what chance looks like. The results cluster around the expected value, here five heads, but rarely land on it exactly and almost never repeat. Understanding variation stops a child expecting chance to be tidy, and it is the reason we repeat experiments and look at many results together. With events ordered on the scale, trials conducted and tallied, expected results predicted and variation understood, a child can both describe everyday chance and investigate it like a scientist.
Quick self-check
1. A bag holds only blue marbles. Picking a red one is...
2. Rolling a 7 on an ordinary six-sided die is...
3. A fair coin is tossed once. Landing heads is...
4. A bag has 4 red marbles and 1 blue. Picking red is...
5. A fair coin is tossed 20 times. The number of heads is most likely to be about...