Lip reading is easiest when talking with only one person, with good lighting on the face of the speaker. 

Trying to lip read in even a small group is not easy; even on a project about disability awareness, people can forget to remember to speak only one at a time, looking at the lip reader: when the conversation gets interesting, they automatically focus on the ideas, and forget the way they speak. When two (or more) people speak at the same time, whose lips can the lip reader look at?  It is best to agree before the group starts who will be responsible for reminding the group to speak clearly, one at a time...

In a class of 20 students, a lip reader can get forgotten: 'One of the quiet, silent ones' - who will not be able to ask when she doesn't understand ... if she hasn't heard.  The student needs to be able to tell the teacher what she needs, when she doesn't understand, and how she wants to study.