Centres are required to assess all internally assessed work in accordance with the assessment criteria in the specification and any guidance contained in the subject-specific instructions for the conduct of examinations. Internal assessors must show how the marks have been awarded in relation to the marking criteria defined in the specification. Guidance on the marking of work is given in the specification.

You can find detailed information about internal assessment in chapter 21, section 5 (p546 onwards) of the information manual. This section covers the presentation of work, centre consortium arrangements, minimum requirements, requests for special consideration, lost work, standardisation of assessment, moderation by Edexcel and feedback to centres. 

This chapter is available for download from this page if you prefer to view it online.