You as the teacher have the responsibility to keep the lesson focused. Your student might want to chat with you. You might have become friends over the course of many years of working together, but they are still paying you. They won’t say it, but they want you to keep them focused.
Interrupt your client mid-sentence. If you can not get a word in, have the courage to just start cueing them. They’ll stop talking so they can hear you. After all, they want you to teach them. They wouldn’t be there otherwise.
Challenge them. Maybe they can do an exercise in their sleep and don’t need much focus to do it right. (Footwork again?) How about a single leg version, on the toes and in high heels. Or how about internally rotating the legs, like the letter X. Anything that wakes them up and gives them something to think about (other than their child’s soccer game.)
Forget to mention the name of the exercise. Your regular students know the names of the exercises, and it’s a great short cut to be able to say “Let’s do Bridging” or “Breathing” instead of cueing every single body part. But if your student rushes into the exercise without preparing themselves, then it might be helpful to teach the movement step-by-step instead. “Press all three corners of your feet firmly into the mat. Inhale to prepare. Exhale, roll your pelvis towards your shoulders and articulate your spine up off the table one vertebra at a time until you reach your bra strap.”
Teach a breathing exercise, such as the Hundred or Ron Fletcher's clock or Breathing with a strap. You can't talk when you're focusing on your breathing.
Pick a very slow and deliberate breathing rhythm. When you focus on your breath, it’s impossible to talk at the same time. In the example of Bridging, you could teach Segmental Bridging where you only move one segment at a time on each exhalation. Like this: “Inhale to prepare, exhale to roll your pelvis towards your shoulders until the lower back meets the mat. Inhale while you stay there. Exhale, tilt your pelvis up towards the ceiling and lift just one vertebra higher. Inhale and hold the position. Exhale lift one vertebra higher, tail bone leads the way, chest stays heavy. Inhale into your back.” Etc. You’ll be talking a lot, but they won’t.
How do you bring your student’s focus back to the work?