This is a low stress way to group students.
Requires two decks of playing cards.
Set up: Suit cards with like numbers (7 of diamonds with a 7 of diamonds) from the two decks of cards.
Option #1: Shuffle matched cards together making sure there is an even number of cards for the class size. Hand participants a card as they enter the classroom informing them to find their perfect match.
Option #2: Using a single deck of cards adjust the deck to reflect the class size (24 students 24 cards make sure there are 4 like cards ex: 4 Aces, 4 Kings, 4 Queens, etc). You can have the participants shuffle and split the deck if desired. Everybody selects a single card and then group up with three other students with like numbers.