Boy taking science exam

Grade Boundaries – Why Do They Move?

Grade boundaries are always the cause of much speculation. Are they high? Low? Does it mean anything?

The bottom line is that students think that low grade boundaries are wonderful – but are they? And does it matter anyway?

Grade boundaries are set so that the harder an exam appears, the lower the grade boundaries become. This ensures that if a student were to sit the same GCSE for five years in a row, they would always get the same grade. If the paper is particularly difficult, less marks are needed for the same grade, and so the grade boundaries are lower.

If you look at a normal distribution curve, the classic bell-shaped curve (the Gaussian distribution for the statisticians) there is clearly a mean (the point in the middle when the frequency is highest) and the results are evenly spread about the mean with a symmetrical shape like a bell. Very many measurable parameters show this bell-shaped curve. The length of leaves on a particular tree, the shoe size of the children in year 7 at a secondary school, the number of eggs laid by a chicken in one year, and even the ability of 16-year-old students to impart chemistry knowledge.

So, a paper is deliberately designed so that less able children will get a bare pass, middling children get a middle mark, and very bright children (with an ability to both retain information and apply the knowledge that they have to a new situation they may never have come across before), to get a high mark.

To me, the fluctuating grade boundaries are a good thing, they mean that children able to pass in 2015, can be compared favourably with children able to pass in 2018, even if the 2015 exam paper was much more challenging.

Grade boundaries are often lower when there is a syllabus change. Then, after a year or so and the teachers become more proficient with the new content, and become familiar with the question styles, children sitting the exam achieve higher grades. Thus, the grade boundaries increase to reflect what is effectively a shift in the mean mark achieved across all of the children who have sat the exam.

So, if the grade boundaries were lower the previous year compared to ‘your year’? it really doesn’t matter because regardless of the paper or the year, the grade that you have achieved would have been the same year upon year – you would still sit in the same place in a normal distribution curve of all of the children sitting the GCSE with you.