My son joined Beta Club at the end of 6th grade last year. Our Beta Club meets twice a month before school -- DS says the meetings are kind of boring. However, they also take a group of 7th and 8th graders to the Senior Center once a month to serve lunch to the seniors, DS said that was kind of ok. He said that the seniors were nice at the beginning and talked to the kids, but then the seniors started conversing among themselves and it was like the kids weren't even there.
They also have collected money and bottled water for Haiti and have helped out a few other causes over the course of the year.
It's an honor to be chosen, congrats to your son!