No More Than 5 Players Per Game
It has proven most effective when no more than 4-5 students play with one game. Anything more than that reduces the learning effect.
Therefore, in class (e.g., during substitute lessons), I always worked with 5-6 games.
It was a lot of fun, and it allowed for wonderful differentiated work – students who had hardly any problems with German played with the blue cards (these contain the 150 most commonly misspelled words, such as "Chrysanthemum"), while the other players practiced with the "easier" words, oh excuse me... I meant played, of course.
The class set contains 5 games. So, this is enough for 25 students.