I have known [name of student] for the past [number of months, semesters, years] as [he/she] has taken the following courses which I teach: [list courses, give brief description of content of course] . As [his/her] professor, I have had an opportunity to observe the student's participation and interaction in class and to evaluate the student's knowledge of the subject matter. I would rate the student's overall performance in these subjects as [below average, average, above average]. This is evidenced by [his/her] grades— [state the grades] .
Problems with references
Your employment history tells a story. One of the most common questions about references is "Why no references from this recent employer?" You may well have a very good reason for that situation, but the gap is still noticeable, and needs filling. In some cases you actually have better references from other sources. You may never want to see your recent manager again.
Whatever the reason, prepare a response to this inevitable question, so you don't trip over it during an interview. You may be able to get a reference from the prior employer from another source. You may want to point out that under the circumstances of your departure from that employer you didn't consider it appropriate to ask for references. You can then add that one of your other references is a fully qualified person to provide references in relation to the job.
In some professions and industries, your references are themselves a quality check on your application. Working for big name employers is a real career asset, and so are their references. However, the same criteria apply for choosing your references, with some additional considerations created by your line of work:
Business references: Target your references, using appropriate managers or supervisors in relation to the new job. If you're going for a sales job, you'd use a sales manager as a reference.
Technical jobs and IT job references: These jobs really do involve speaking another language, and your reference must be able to deal with any technical questions about your work. Technically qualified managers or highly qualified technical experts are the best references.
Academic references: For postgraduates, academic references in some professions and sciences can be difficult/impossible for those outside the profession. Your reference must be someone who can deal with advanced questions at this level. A former lecturer or a recognized expert in the field is the best reference.