Adult students are typically older and have already spent a number of years working as professionals. According to the book "Teaching, Learning and Assessment for Adults: Improving Foundation Skills," adult students are often overrepresented in the categories of minorities and low-income, and often did not have a very good high school education. Some of those students may have also graduated high school thanks to a GED. Knowing who the students are can help in knowing their background and the challenges it took to get to college. Even a basic grammar or basic knowledge test might help.
Giving a test is an easy way to find out if students understand the material and if test scores fluctuate throughout the term. Many adult students have trouble with tests, mainly because they've been away from the practice of test taking for some time. Written assignments also help to determine if the student is having trouble with grammar, spelling, content, structure or even research skills. Should there be problems in any of these areas, the teacher can step in to help.
Have students keep a learning journal throughout the course. This allows the instructor to get a better sense of what the student is thinking about and what the student is learning (or isn't learning or is having trouble understanding). Because learning journals are often reflective, the instructor will learn how to better teach the course, especially if the same themes are mentioned by several students. While learning journals are popular in undergraduate education, they might be more effective when dealing with adult learners because of their experiences; this provides much needed insight to the instructor in the way of future course development.
Since adult learners are often working full-time (some even having their education paid for by their employer), instructors should contact the student's employer to find out if the goals are being met in academia. According to the book "Best Practices in Adult Learning: A Self-Evaluation Workbook for Colleges and Universities," employers often have a "critical stake" in the learning process because they benefit immediately from the education of the student. Their evaluations help the college become stronger in their teaching and how they prepare future students.