I've collected and collated 18,600 GCSE 9-1 grades across 22 subjects from schools comparing the last predicted grade to the grade attained in the 2019 summer exams.

The accuracy of these predictions was 40.3%.

84.7% of grades predicted were within 1 grade of actual result.

Here's a by subject chart - more analysis to follow later

I'm still keen to add more data from schools to the analysis... here's how: https://dataeducator.wordpress.com/2020/03/21/accuracy-of-predictions-research/

For those who like the numbers. I am going to release all this in due course.

By student group:

6 students so far out of over 3000 attained exactly the same grades as predicted across all their subjects.