One of my favorite beginning of the year activities is a card sort that we do that reviews if different numbers are irrational or rational. Students are placed into groups of 4 and have to reason with one another about the placement of each number.
Here are a few groups placing their numbers:
Here are some example numbers we had:
Here are some finished products:
This was a great activity to get students use to classroom procedures and routines. You can find the activity here: http://map.mathshell.org/lessons.php?unit=9105&collection=8&redir=1
The activity was in groups and went through each one large group. I had students explain why they put them in certain categories and had a classroom discussion if they agreed or not. Some could be put into more than one category depending on the explanation. It was a fun experience.