I have a little trick I use to get kids to isolate a passage. It’s called the “ten penny” method, and it also works with M&Ms that they can eat if they finish successfully.
Take ten pennies or M&Ms and line them up on the left side of the music stand. The student chooses a section of music that they think they can play perfectly with no mistakes. If they play their section perfectly they can slide a penny from the left side of the stand to the right. The goal is to play the passage perfectly 10 times in a row, and slide all the pennies from the left to the right. If they make any mistakes along the way, ALL the pennies go back to the left side.
Usually the first time I try this with a student they choose a section that is too big, and they play it too fast. They soon realize that to finish the exercise they must choose a small section and play it very slowly. The kids seem to really like the challenge of this exercise and it’s a good way to get them listening to whether they are really playing perfectly, rather than just playing something over and over again wrong or sloppy.