Don't neglect the Ten Minute Math activities. Some of these can stay out all year in the back of the room as part of a learning center, for example. Most are easy to set up, easy to learn and provide opportunities for differentiating instruction without lots of teacher preparation. They are especially important if the students coming to you in fifth grade did not have much experience with the program in previous grades. These activities will get them and you used to the format of the Investigations program fairly quickly. If you are looking for a single source for all of the Ten Minute Math activities from grades 3-5 in a single booklet, try Dale Seymour Publications. Once you have the booklet you can set a few up that your students may have seen in earlier grades - just modify them with larger numbers, decimals, geometric figures, etc. Good luck!
