This spring I used the Packages and Groups book and was very pleased with the activities and the results. My students enjoyed the multiple tower activities and really grew in their understanding of clustering with the double-digit multiplication problems. One activity I really liked was the Making a Multiplication Table. (Sessions 1 and 2 in Investigation 1). Students use the array cards to fill in a blank multiplication table- a 12x12 array. Doing this helped them to prove why the multiplication table works. It was a fun and engaging activity that really cemented their understanding of arrays and multiplication. As an extension of this activity, I had them revisit perimeter and area. We used just the arrays that made 36 and colored each one a different color. (1x36 and 2x18 didn't fit so we just talked about how they would look on the paper.) Then I asked them to imagine that they had to carpet and put a wallpaper border on each room. They estimated first, and were very surprised to "see" that the long skinny room (probably a hallway) would need more wallpaper than the 6x6 room.
If you haven't used this book yet, I highly recommend it! Lee Ann Pruske Milwaukee, WI