Trust a student's peers to provide a fair and accurate assessment of her work. If a class relies on group activities, a peer evaluation form could be included as part of the assignment. Each member of the group will have to rate the other group members' participation in and contribution to the group project. Students can be trusted to provide fair assessments of their peers because they expect to be assessed fairly themselves.
Keep an up-to-date, detailed grade book for each class. In it, keep track of class absences, tardiness, preparedness, students' adherence to deadlines, and class participation. A student with a high level of professionalism will perform well in all areas. These students understand that a classroom setting is a like rehearsal for the professional world and make every effort to exemplify responsibility.
Test your students' abilities and professionalism with an exercise for practical application of the field of expertise. If in a medical field, you could plan a mock patient diagnosis session to evaluate students' treatment of patients, aptitude for the subject matter, and grace under pressure. A student with a high level of professionalism will not crack under pressure; instead, he will calmly work the problem until a solution is found.
Interview students about their own performance in a class or given situation. You may be surprised at how honestly professional students will evaluate themselves. This exercise will also assist the teacher in pinpointing any problem areas in the individual's education and the teaching methods used.