If you have never done any type of classroom assessment, then the best place to start is with one of the simple Classroom Assessment Techniques (CAT's) as described in the book by the same name by Cross and Angelo.  This document will explain the rationale as well as several of the most common techniques found in their book.

First, several principles of assessment should be considered before choosing what to assess in your classroom.  The main goal of assessment is to be learner-centered such that the focus should be on improving the quality of the learning process.  The assessment should also have faculty ownership: you decide what to assess, how to assess, and what to do with the results.  If the feedback loop is completed properly, then the assessment is mutually beneficial to both the learner and the teacher.  Lastly, most classroom assessments are done anonymously and are not graded.  This assures students the ability to give honest, constructive feedback on what they are and are not learning.

Classroom Assessment is based on seven assumptions that also must be considered before doing any type of assessment.  Many of these issues are things that most instructors are aware of, but can also be a good reminder.  These seven assumptions are:

1. The quality of student learning is directly proportional, though not exclusively, to the quality of teaching.  Thus, if you can improve teaching, then learning will also improve.
2. To improve teaching, instructors need to make their goals and objectives explicit to their students.  Quite often, faculty believe that their goals and objectives are crystal clear only to find that many students still misinterpret them.  The more clearly you define these, the better the learning environment will be.
3. To improve learning, early and often feedback to the student is critical.  In addition, students who can self-assess will almost always be more successful.
4. The type of assessment most likely to be successful is one that touches on a previous problem area.  Have you ever said, "I don't understand why students can't seem to grasp this topic?"
5. The process of systematic inquiry and intellectual challenge can be powerful renewal factors for even experienced faculty members.  Classroom Assessment can cause even "old dogs" to consider "learning new tricks."  
6. Classroom Assessment does not require any special training - anyone can do it.
7. By sharing techniques and experiences with other faculty and involving the students in your classroom, faculty can improve the quality of learning in the classroom.  When this occurs, faculty satisfaction (and student satisfaction) increases.  

If you have never used a CAT, then the advice that most seasoned CAT users would give would be to start small with either the One Minute Paper or the Muddiest Point (explained later).  Pick one or two of your classes to try a CAT on.  You do want a class that has a critical mass (more than ten students), which helps to preserve the anonymity.  The area or topic that you choose to assess should be one that, in the past, has caused difficulty for the students.  When you administer the CAT, explain carefully to the students what it is and WHY you are doing it (to improve the learning process).  As soon as possible, read through all of the student responses.  You might want to make piles of similar responses to identify any patterns.  Then, before the next class meeting, prepare a response to the class.  It is not necessary to address every response, just those that appeared most often.  Once the cycle has been completed (teacher > student > feedback), reflect on the experience.  Was the CAT successful?  Why or why not?  Don't be discouraged if it did not go well.  Many teachers fail the first time they try this because their instructions were not explicit enough.  

Some common CAT's explained (briefly):

• One Minute Paper: asks two questions – (1) What was the most important point of today’s lesson?  (2) What important question remains unanswered?  This allows even the meekest of students a forum to respond to your lecture / discussion.
• Muddiest Point: asks the question – What is the muddiest point of today’s lecture / discussion?  This provides information on what they thought was the most un-clear part of day’s activities.
• Background Knowledge Probe: used in the first few class meetings.  Answers the question of what the students know coming into the course.  Can also be used before any new unit or to gather information about student opinions.
• Misconception / Preconception Check: find hidden barriers or biases to learning.  Best used in areas where students have “life” experiences.
• One-Sentence Summary: challenges students to answer the question – Who does what to whom, when, where, how, and why?  This will allow teachers to find out how well students can summarize large chunks of information as concisely as possible.
• Application Cards: are used after a student has heard or read an important principle, theory, or procedure.  Then, the instructor hands out index cards and asks the student to write down one real world application.  This technique prompts students to apply the knowledge that they have just learned.

These represents only a brief synopsis of six of the fifty techniques described in Classroom Assessment Techniques, by Thomas A. Angelo and K. Patricia Cross published by Jossey-Bass.  Several copies can be found in Instructional Development Center as well as in many faculty offices.