What marks do you need to get a C grade in maths?
Although new style GCSEs start this June with marks graded 9 to 1 (9 being the highest and 4 being equivalent to a low C) it is unlikely that the marks you need to gain across the paper will change much. Students taking the Higher tier paper from Edexcel or AQA will need to score about 32% while students taking the Foundation tier paper will need around 71% to secure a C grade.
If you are a borderline C/D grade student it is tempting to think that sitting the Higher paper and aiming to get a lower percentage is the way to go. However, in my experience (and I mark for one of the exam boards) weaker and less confident students can struggle to understand how to answer questions on the Higher paper. Even if they can do the calculations required they have difficulty applying the correct calculation to the question. They often also assume (not always correctly) that they will be unable to attempt questions after the staples on a Higher paper.
Struggling with maths is often an issue of confidence and I have found that my borderline students who opt for the Foundation paper often immediately feel more confident that they can answer the questions in this paper. This confidence makes a huge difference and these students have all achieved the C grade they need.