Kahoot: Ghost Mode

Kahoot is an assessment tool that can be used with BYOD or school owned devices.

How ghost mode works:
First, run a Kahoot game as you normally would. At the end of the game select "ghost mode" to run the game again. In ghost mode students play against their own scores from the previous game. Then when you run the game students will be competing against the "ghost" version of themselves from the previous running of the game. For example, I play a game as a student in the first running of a game then in the second running of the game I'll be competing against my previous score as well as those of my classmates.

This article explains all about it.