Lynnie,
I'm so sorry you have had problems like this, they can be quite disheartening. I am so very grateful now that I have taught for nearly 30 years, have learned a lot about human nature, and how to handle the too often problem student.
A good lesson came in an early class where I had one particular student I despaired of ever getting through to. I didn't think she'd ever catch on. At one point while sewing strips together, after sewing several pairs, she all of a sudden started sewing them together perpendicular to each other rather than side by side! (wth?!) We made it thru the class with much intervention and frustration on both our parts.
She showed up at a monthly meeting of our bee -- sort of a 'club' of former/current students who met in my home -- about 2 months later and was so joyful to show us her show-and-tell. She had made, AND FINISHED, a bed size Bear Paw quilt with a pieced backing with a trail of bear paws up the back through the middle!! I was so surprised, touched, thrilled for her, and grateful that I had had a part in her "aha' moment. Never mind the fact that the bear's paws were pigeon toed...it was a design decision, I could tell myself, and I never said a word about that!
She went on to become such a quilter that her DH actually adapted a trailer as her traveling sewing space for the many weekends they had to drive several hours to assist their aging parents for the weekend.
You can only imagine how thankful I am that I didn't give up on this student or on teaching. I began a "pat (on the back)" folder where I've kept decades of thank you notes from students; that is something I pull out and look over every once in a while when I'm feeling down.
My favorite part of teaching is seeing the light come on in a student's eyes, that "aha" moment when a technique makes sense and opens a whole new world to them.
Jan in VA