I once spent 20 minutes of a 50 minute class trying to get Japanese students into groups. This only happened because I refused to accept the groups they already had.
My plan, simple as it seemed, involved putting the students into one of four groups. To do that, I implemented a simple system of assigning numbers: You’re 1; You’re 2; You’re 3; You’re 4; etc. I encouraged the students not to forget their numbers. After everyone had a number, I pointed to various corners of the room and said “Ones here; Twos here; threes here; fours here.” and stood back with my arms crossed a sense of smugness.
Twenty minutes later I had no fours; three ones, four threes, and everyone else was a two.
The Japanese teacher working with me translated into Japanese and after another five minutes we had something resembling groups but little time to do the activity.
My mistake was misunderstanding the importance of pre-made groups. Basically, all Japanese Junior high classrooms, especially in public school, are organized in alternating rows of boys and girls. With various magic words, the teacher can quickly organize the room into pairs (Anál nathrach); groups of three (orth’ bháis’s bethad) and groups of six (do chél dénmha). Something like that. (Bonus points if you are old enough to recognize the spell and know what movie it came from. Don’t tell your parents you watched it when they were asleep, though.)
I also misunderstood the managed teenaged politics involved with the groups. This month Maki doesn’t like Koji and will never be in a group with him but she does like Ami but Ami doesn’t like her but also won’t be in a group with Akiko. Next month all that will change and everyone will hate Ami.
When I used basic randomness to assign groups I was putting people in groups who refused to be together.
The best part is, because I didn’t use the activity, I already had the next class planned.