I have some ideas about assessment. My first thought is that assessment is a complex topic with multiple facets. My second thought is that accurate assessment and appropriate use of assessment results probably require as much professional development as effective teaching of math.
We teachers have "the responsibility to understand and monitor" the growth of our students (NCTM). "The more comprehensive our assessment, the better able we are to make appropriate adjustments in our teaching and to communicate students' thinking, abilities, and accomplishments to others." (NCTM) Understanding and monitoring the growth of our students means that we have content knowledge as well as knowledge of the mathematical development of concepts and skills.
Investigations lessons provide opportunities for students to learn mathematics with deep understanding. Every lesson is a source of informal assessment, and teachers are offered "Teacher Notes" and "Dialogue Boxes" to inform us about what to watch for and how to evaluate what is observed. Our formal assessments must be tasks that will assess this deep understanding. We need to know students' number skill and computation level, but our focus should be on how they are able to use their skills in problem solving situations. We need to consider what we learn from open, rich assessment tasks versus closed, fill-in-the-box type problems.
If students have experienced open problems for just a short time, they will need to learn how to provide a "thinking trail", so they can show their understanding in their daily work and through the assessments. Then we, as teachers, need to learn how to make accurate instructional decisions and inform others about the students' level of performance based on what we learn from their oral and written work.
Investigations offers embedded assessments with the Teacher Notes suggesting evaluation of evidence gathered from the assessments. End-of-the-unit assessments are provided in the Assessment Resource Book. There are rubrics posted online to correlate with these assessments. This is assessment and evaluation that looks different from traditional textbook chapter tests.
The assessments you choose to use in your district will also depend upon the type of reporting system you have in place - are you "standards-based" or are grades given according to averaged percentages? If your learning targets are aligned with the mathematical emphases in Investigations that you are using as the basis for your instruction, you will find assessments available in the units. If your district requires closed, skill-based, computation-type assessments, those can easily be added, but the information gained from those assessments may not give accurate direction for your instruction using Investigations.