I have not taken private lessons before but I do heard from my previous instructors that there are private candidates whom switch to back to school and they re-train the whole lessons again. dont't know if the candidates requested or it's a must though.
However, if you need to retake the whole thing again, I think it's worth it and with your experience already, they will probably fast track your lessons. I took about 27 lessons and pass my driving test in 1st attempt. I did not specify any particular instructor.