Precision vs. Accuracy: Analyze Your Throw Grouping
Each student tosses bean bags onto a grid with axes, records the coordinates of each landing and calculates the center of their grouping and how spread out it is. That shows whether their problem is accuracy (aiming off-center) or precision (inconsistency), so they can apply the right fix.
How to play
- Concept with four drawn targets: accurate and precise, accurate but scattered, precise but off-center, and neither (4 min).
- Group setup: crossed tape axes on the floor with the target at the center and marks every 20 cm; throwing line at 5 m (4 min).
- Set 1: ten bean bags per student; the partner records each bag's (x, y) coordinates in centimeters (6 min).
- Math: center of the grouping (mean x and mean y) and spread (average distance from each bag to that center). Diagnosis: if the center is far from the target, fix your aim; if the spread is large, work on your routine (6 min).
- Set 2 with the chosen fix, then compare both measures (8 min).
- Wrap-up: each student writes what changed and why (2 min).
Rules
- Nobody steps onto the grid until the pair has finished measuring.
- Bean bags stay where they land until the coordinate is recorded.
- Underhand throws, always from the same line.
- Data belongs to each student; no public rankings.
Variations
Easier
Grid with 50 cm squares; record the square instead of the exact coordinate.
Standard
Coordinates in centimeters, grouping center and average spread.
Harder
Also calculate the standard deviation of x and y separately to see whether the error is more side-to-side or short-long.
Adaptations
- Visual impairment: the target makes a sound before each throw, and the partner describes the cluster on a raised drawing made with modeling clay.
- Limited mobility: throw seated or use a ramp; the analysis is identical.
- Math difficulties: a calculation template on the teacher's device or a worksheet with guided steps.
Learning goals
- Distinguish accuracy from precision in a motor task.
- Calculate a center point and a spread measure from your own data.
- Choose the right fix for each type of error.
Equipment for a class of 25
- bean bags: 30
- masking tape: 3
- measuring tapes: 6
- score sheets: 30
- calculators: 6
Teacher tip
Team up with the math department: this fits their statistics unit and they love real data. Measuring takes longer than you'd think; if the group is slow, have them measure only x and y with the tape, not the diagonal distance.
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