Hello Tim,
Reinforcement from instructors is very important. Your unfocused students generally need reinforcement to increase their knowledge base. I will let the unfocused student know that I as a student was ALWAYS focused, and I would have private meetings with the unfocused students to tell them my reasons for ALWAYS being a focused student, and perhaps the conversations will help the student become focused. I will then find a colleague that had an opposite experience than mine so that the colleague could present the presentation based on what the unfocused student was going through.
Patricia