As part of continued efforts to ensure inclusivity in assessment, OCR has developed a set of accessibility principles for question design in GCSE Science examinations, which has been applied since 2018. The principles are intended to help ensure that all students can demonstrate their knowledge, understanding and skills to the best of their ability. The aim of this research was to consider the effectiveness of the accessibility principles by investigating students' perceptions of question features in terms of accessibility. Two versions of a short test were constructed using questions with and without the accessibility principles applied. Students in Year 11 (aged 15 to 16 years old) from four schools across England attempted the test and, of these, 57 were interviewed afterwards. Students were asked about question design features relating to the different accessibility principles and encouraged to talk about how accessible they felt the questions were and why. The results revealed that for most of the question features explored in this study, students' perceptions of accessibility tended to align with expected effects. However, for three accessibility themes, the findings were neutral or mixed.