For the teacher...
-- a roll of paper towels for their help in "cleaning up" or "tackling" the problem.
-- a short thank you note for their help in coming up with a plan for improving things.
For the student...
-- a box of paper clips or rubber bands because "together we're are going to hold it together"
-- a pad of cute sticky notes to help you "stick with it"
[If you used one of these earlier in the year, choose a different one now.] The point is just to let both your child and the teacher know that the issues you discussed at parent conference are remembered and that they can both count on you to follow-through and help resolve the problem. The child needs to know that you will be there to help, not just to nag or scold. The teacher needs to know that you can handle bad news as well as good, that you will work with them and with your child.
As a veteran teacher I can assure you that the teacher wants every single child to succeed. Happy, successful children are easier, more fun, and more rewarding to be working with each day. Experiencing success and feeling hopeful creates a wonderful synergy of energy and achievement in a classroom, regardless of where each individual starts the year. Working together as a team helps make that happen.