Marks, scores and grades: scaling and aggregating student assessment outcomes

The term marks conflates the concepts of scores (raw test performance) and grades (level of performance). Neither scores nor grades represent interval scales, and therefore properly speaking arithmetic means should not be calculated during aggregation. The distributions of scores from a variety of kinds of assessment are considered, and ways of converting scores to grades are discussed. Methods of aggregation are also considered, and several strategies for implementing these via spreadsheets are made available. It is recommended that:

1 Scores should always be converted to grades before aggregation. The process of converting scores to grades requires both subject-specific skills, and familiarity with educational principles.

2 Whatever grade scale is used, it should be readily distinguishable from scores.

3 The median should be calculated as the measure of overall performance, not the arithmetic mean.

4 The interquartile range should be calculated as the measure of dispersion.

5 Students should be informed of both their score and grade for each assessment.

6 Where possible, assessment should report performance by individual assessment, not by a single aggregated mark.

7 When aggregation takes place, it should be possible to aggregate student performance by type of assessment as well as by academic subject.

8 Students who perform inconsistently should receive particular scrutiny during assessment.