Here's the kind of sheet I use with my students to write down their bonus points.
Students form a team of 4 and gain bonus points during the lesson by participating and achieving written tasks. The first team to reach 20 points wins and stops the other teams' counters. I then pass in the groups to calculate and write down the number of bonus points they have and transform them into a mark, out of 20.
Hope it helped! Don't hesitate to ask questions if you wish to!
I've uploaded other sheets on the site.