Computing, like every other subject, is assessed by class teachers.
The screenshot below (from the CAS booklet) outlines the program of study statements broken down into Computer Science, Digital Literacy and Information Technology. They have been arranged so that a progression in each strand is easy to follow and then teachers, by gathering evidence of pupils work, can make judgements as to where pupils sit on the scale. It is therefore easy to identify a pupils capabilities within Computing and where the gaps in their learning appear. Teachers can gather evidence of pupils work through screenshots, saving work in specific folders, audio and video files and through observations during lessons.