Kevin, while John had had "had", had had "had had". "Had had" had had a better effect on the teacher.

To explain in more detail:

John had had "had" - as in John previously had "had" as his choice.

However, Kevin had had "had had" - as in Kevin previously had "had had" as his choice.

"Had had" had had a better effect - as in "had had" managed to achieve a better effect.