What does a z score of -1.00 indicate about a student's performance?

A z-score is a statistical measurement that describes a value's relationship to the mean of a group of values. A z-score of -1.00 indicates that the student's score is one standard deviation below the mean for the entire group.

This specific z-score can also be interpreted in terms of percentile rank. Since a z-score of -1.00 places a student's performance below the average, it typically correlates to a percentile of about 16%. This means that the student scored better than approximately 16% of their peers, as the negative z-score reflects a position further from the mean in the lower tail of the distribution.

Understanding this percentile rank is crucial for interpreting z-scores, as it provides a clearer view of how a student compares to others within the dataset, enabling instructors and students alike to gauge performance relative to peers.