The Experiment

In the video, Professor Wiliam detailed a seminal study by Ruth Butler (1988) involving 12 classes of students. The teachers taught the same lessons and used the same materials, but they provided three different types of feedback:

1. Grades Only: A numerical score (e.g., 7/10).

2. Comments Only: Diagnostic advice on how to improve.

3. Grades + Comments: The "best of both worlds" approach.

The Results

The findings were stark and counterintuitive for many educators:

• Comments Only: Students achieved a 30% gain in learning.

• Grades Only: Students achieved 0% gain (no learning took place).

• Grades + Comments: Students achieved 0% gain.

The Conclusion

The research proves that the presence of a grade completely "washes out" the beneficial effects of the comment. As Wiliam notes :

"The logic of 'A' [the students getting both] is you get the best of all possible worlds... [but] the students who got the grades and the comments did the same as those who just got the grades"