My class has 2 sets of buddies: Kindergarten Reading Buddies and 1st Grade Math Buddies
When second graders visit kindergarten they have to be the "big" kids and read. Many of mine think teaching is fun so they point to the words for their buddy and help them to read their books too. As the kids get better at working together they will be able to do activities like share a mini book report type project with their buddy.
I love having good readers and they love reading!
When we visit with 1st graders we share math problems. The first graders had support in solving and explaining their work while the second graders really had to think and carefully explain what to do. We planned for 15-20 minutes and 30 minutes flew by with kids on task, and these groups are not known for being calm and on task!