There are several resources that will help you look at student work and observe students as they work built into the Investigations curriculum. Be sure to pay special attention to the sections called:
Assessment in this Unit (at the very front of the unit) Observing the Students Teacher Checkpoints Teacher Notes
The assessment booklets for each grade level are very helpful.
I also find the section at the beginning of every unit - Assessment in Investigations very useful. The section describes mathematics behaviors common to all mathematical experiences when students are think and communicate as mathematicians.
When you start, read through the sections and choose the mathematical emphasis that makes sense for your students. What do you want to know about your students? Which Teacher Checkpoint will help you most at the time? You can choose different teacher checkpoints as you get to know the needs of the students.
Other resources that have been developed by different school districts can be found on the Scott Foresman site. They might not fit your needs exactly, but they might help you get started with personalizing your own assessment tools.