It has been my experience that taking the time to listen to your student and obsserve their behavior, you find those who have lost their way and are just "skating" by in class. I find that speaking with them after class privately, I ask them what is affecting them or their personal life. Most of the time by just listending, or gentle persuasion I can get them to open up. Usually I relay this information on to our Program Director so he can speak to him/her about what is hindering them to stay focused.
Yes, some issues such as immediate health issues can't be helped; but, for those who are just mad because someone didn't come running like they wanted , instructors find the student can get a bit testy with them when they feel their needs are not being met.