Standard score is a statistics term. The standard score shows how far away from the mean a score falls. It is also known as a z-score. Using a z-score table, you can find where the score falls on the table and figure out what percentile the score falls in. This is a way of standardizing tests in order to curve the scores to fit around the mean. If everyone does poorly on a test, the score distribution will curve up to fit around the average score on the test.
Find the mean and standard deviation of your data set. For example, assume you have a data set with a mean of 24 and a standard deviation of 5. You want to find the standard score of 28 in the data set.
Subtract the mean from the data for which you want a standard score. In the example, 28 minus 24 equals 4.
Divide the difference between the data and the mean by the standard deviation. In the example, 4 divided by 5 equals a standard score of 0.8. You can use this score on a z table to see where it falls as a percentage of the rest of the scores.