This paper aims to assess the impact of using GCSE grades as a primary outcome in educational evaluations and trials, compared to using marks. The choice of grades or marks is relevant as many evaluations use GCSE performance as an outcome measure. For such evaluations, the National Pupil Database (NPD) is used as a source of data by the vast majority, and it contains grade information only; no information on the underlying mark distribution is available. The use of the NPD has largely been a pragmatic choice, as historically it has been comparatively easy to access grades via the NPD than gather marks (or indeed grades) from schools or awarding organisations. However, there has been little consideration of whether only having access to grade information, as opposed to the marks, has consequences for evaluations. Data was provided by the Joint Council for Qualifications detailing mark distributions for GCSE English Language and Mathematics in the summer 2019 series. [An additional collaborator of this report is AlphaPlus.]