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A Project-Based Unit on Probability: Planning It Week by Week (New Zealand)

A four-week probability project built around designing a school gala game, with weekly milestones, group roles and a marking split that keeps it fair.

Probability taught as a set of calculations produces students who can find the chance of drawing a red counter and have no idea whether a game is worth playing. A project fixes that, because a project forces the question of consequence. The unit below runs for four weeks in a Year 8 or Year 9 class working at curriculum levels 4 and 5, and it ends with something the school actually uses.

The driving question and the final product

The question is: can our group design a game for the school gala that is fun to play, obviously fair, and still makes money for the school? Every word does work. Fun forces a playable design. Obviously fair forces the group to communicate probability to a parent who has not studied it. Makes money forces expected value, the concept most classes never reach.

The final product is a working game stall with three artefacts: the physical game, a one-page probability analysis, and a sixty-second pitch to a panel of your choosing. Groups of four.

Week one: play badly designed games

Do not start with theory. Start with four stations of deliberately broken games, each either impossible to win or impossible to lose. Groups play, get annoyed, and state what is wrong in writing. That written complaint is your baseline assessment.

The teaching in week one is sample space and theoretical probability, in two short lessons rather than four, because the project supplies the motivation. Milestone: each group submits a one-sentence game concept and its sample space. Reject any concept running to more than about twenty outcomes; ambition here is the enemy of completion.

Week two: build it and test it

Groups construct a prototype and run at least sixty trials, recording every result. Sixty is roughly where experimental results start to resemble theoretical ones, and watching that convergence is worth more than being told about it. This is also where groups discover their game pays out far more often than they expected. Structured experiment material saves you building recording sheets for four different games, and Binomial Distribution & Probability Experiments – Grades 7-10 supplies experiment protocols and tally sheets that adapt to whatever the groups invent. Milestone: a completed data table and a comparison of experimental with theoretical probability, in writing.

Week three: the money week

Now introduce cost and prize. If it costs two dollars to play and the prize is ten dollars, what has to be true about the winning probability for the stall to break even? This is expected value arriving through the back door, and students who could not sit through a formal introduction will chase it here because it is their game and their profit.

The obstacle is proportional reasoning. Groups who cannot move confidently between fractions, decimals and percentages stall completely at this point, and no amount of enthusiasm gets them through it. Where that is the case, run a parallel repair strand rather than abandoning the project, and the Algebra Basics – Ratio, Proportion and Percentage | Math Foundations Workbook | GRADE 5–9 is the material to reach for because it isolates exactly the conversions this week demands. Milestone: a pricing decision with the arithmetic that justifies it.

Week four: refine, pitch, run

Two lessons of revision to the game based on the data, one lesson writing the one-page analysis, one lesson pitching. Then, if the timetable allows, actually run the stalls for a junior class. The difference in effort between a project that gets displayed and a project that gets played is enormous, and it costs you one period.

The strongest groups will notice that their sixty trials were not enough to be confident about anything. Do not smooth that over. Name it as a real limitation and tell them it has a formal answer they will meet in senior statistics, where Hypothesis Testing & Errors – Full Statistics Unit (Grades 11–12) gives the reasoning a name and a procedure. Ending a junior unit by pointing at an unanswered question is better closure than a summary.

Roles, and how to mark a group fairly

Four roles, rotated weekly so no student spends a month cutting cardboard: designer, data recorder, analyst, communicator. Rotation keeps the maths in everybody's hands.

Mark the individual, not the group. Each student submits their own probability analysis, and the group mark applies only to the pitch. That split removes almost every fairness complaint. Feed the individual analyses into your overall teacher judgement alongside your usual evidence, and note what you can see that a test would never show you: whether a student can explain a chance to somebody who does not want to be persuaded.

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