The workload case for outsourcing mock marking makes itself: a class set of thirty Higher tier Maths papers is roughly eleven hours of a teacher's time, usually taken from evenings in the busiest half-term of the year.
The less obvious case: consistency
Internal mocks marked across four teachers produce four standards, however careful the moderation meeting. Departments routinely find half a grade of drift between sets. External marking applies one standard across the cohort, which makes the resulting data usable for setting and for predicted grades.
Intervention data that arrives in time
Marked scripts returned in a week rather than three means the intervention list is written while the content is still fresh. We return a cohort-level topic heatmap alongside the individual scripts so heads of department can see the class-wide gaps immediately.