MobLab games have two modes: Game Mode and Practice Mode. Games played in Practice Mode are not counted towards students' earnings, whereas games played in Game Mode are.
Use Practice Mode to give students a practice round without performance counting against them.
To switch between Game Mode and Practice Mode, simply open the game panel and check or uncheck the Practice parameter. The beaker means the game is in Practice Mode. The game pad means the game is in Game Mode.
You can always change a game's mode, even after the game has been played.