IT is argued that most educators are not trained to create valid assessments of student learning.
Educators choose assessment grading schemes for a variety of reasons.
Some may select a method that reflects the way they were assessed as students; others may just follow the lead of a mentor or instructions given by their institution.
Marking and grading are determined after all student scores for the assignment or tests are assigned. Often called norm-referenced grading, curving assigns grades to students based on their performance relative to the class as a whole.
Criterion-referenced grading assigns grades without this reference. The educator determines the threshold for grades before the assignment is submitted or the test is taken.
For example, a 90 and above could be defined as the base threshold for an A, regardless of how many students score above or below the threshold.
To curve or not to curve is a big question. Curving defines grades according to the distribution of student scores.
Choosing to curve grades or using a criterion-referenced grading system can affect the culture of competition and, or the students’ sense of determined fairness in a class.
Curving grades provides a way to standardise grades but yet, norm-referenced grading can ensure that the distribution of grades is comparable from time to time.
A course with a group of markers or raters, such as “educational studies” that uses a group of undergraduate students in the grading, may also employ a norm-referencing technique to standardise grades across sections.
In this case, standardisation across a group of markers should begin with training the graders.
Curving grades should not be a substitute for instructing the group of markers how to assign grades based on a pre-defined rubric
In addition to standardising grades, norm-referenced grading can enable members to design more challenging assignments that differentiate top performers who score significantly above the mean.
More challenging assignments can skew the grade distribution; norm-referenced grading can then minimise the impact on the majority of students whose scores will likely be lower.
A critique of curving grades is that some students, no matter how well they perform, will be assigned a lower grade than they feel they deserve. Students should have an equal chance to earn an A.
For this reason, some educators do not pre-determine the distribution of grades.
The benefit of using a criterion-referenced grading scheme is that it minimises the sense of competition among students because they are not competing for a limited number of As or Bs. Their absolute score, not relative performance, determines their grades.
Several ways to curve grades can be used include:
* The Bell Curve which normalises scores using a statistical technique to reshape the distribution into a bell curve. An educator then assigns a grade (e.g., C+) to the middle (median) score and determines grade thresholds based on the distance of scores from this reference point. A spreadsheet application, like Excel, can be used to normalise scores;
* Criterion-reference grading is a pre-determined scale, assessments are based on clearly defined learning objectives and grading rubrics, so students know the educators expectations for an A, B, C, etc;
* Clumping is when educators create a distribution of the scores and identify clusters of scores separated by breaks in the distribution, then use these gaps as a threshold for assigning grades.
* Quota Systems, often used in law schools, where the educators pre-determine the number of students who can earn each grade. The educators apply these quotas after rank ordering student scores.
Curving can be used as a tool to adjust grades on a poorly designed test, but consistent use of curving should not be a substitute for designing assessments that accurately assess what the educators want students to learn by the end of the course programme.