How to pair up students? What about trios?
I use two techniques to pair-up or triple-up students.
Do explore alternative ways of doing it. My favourite is to give puzzle-sheets to students and tell them to choose a partner(s)... and anyone chosen must say "yeah!" and start work together. I choose the less extroverted students to give sheets to. That ensures nobody is feeling left out or rejected.
I've had wonderful groups of students who love working together and consistently produce excellent results. In the Infinite Pickle, the trio of grade 5s working on GLUE is a perfect example. Those kids chose to work together. It wasn't random. The results speak for themselves.
The randomization techniques presented here are also worth experimenting with. Be flexible. I often have students who prefer to work alone or in a trio. That's not a big deal. I nearly always allow them that freedom.