When I start to work with students, I want to learn who they are, find out what they (and their parents) want to achieve and create a trust between us. This process shouldn't take longer than one to three sessions. Then it's time to talk about their goals.
I suggest age-appropriate targets, such as, for children in 3rd to 5th grade something like: "response from school teacher is that progress has been made, reflected in grades and homework feedback." For the older students, they seem to be able to tell when they're doing better by feeling more confident about their work, speaking out in class, being able to edit their own writing, etc. But this needs to be stated up front so that they can measure their own progress.
Preschool students don't worry about that, but I council parents about what I would like to accomplish before they enter kindergarten -- that they can recognize and write all letters in uppercase and lowercase block print, spell and write their own name, recognize and write numbers and understand some pretty complex ideas about adding and subtracting recognizable things, know and draw different shapes and know "big, little & middle-sized." And be able to focus on one project for a period of time (from five to 15 minutes) while they can postpone the "fun" stuff.
No matter who the student is, it's necessary for both the tutor and the student to set up guidelines so that we know when I am not needed anymore.