Public service announcement. If your DC got an unexpected result for an Edexcel exam, or if they are close to a grade boundary and you are considering a marking review, ask the school and they can see the marked script for free. This will save you having to worry whether it's worth the cost of a review because you'll have an idea of the outcome beforehand.
Schools need your permission to look at the paper so won't be doing this routinely, you'll need to ask.
qualifications.pearson.com/content/dam/pdf/Support/results-certification/Access-to-Scripts-FAQs.pdf
The deadline for asking for a review of marking is 21st September.