This is the question that many parents ponder when their child is struggling.
I believe that the first place one should get help is from the teacher. If this isn't successful you should get a tutor as soon as possible. The earlier you get a tutor the better for your child. Sometimes parents wait until the end of quarters and/or semesters, but by then there is the deficit of the material from the past which also makes it difficult to help prepare the student for current and upcoming material.
It is natural as students move from grade to grade that at some point they may reach a level of math where they may find some difficulty, and this does not mean that they are no longer a "good" math student. It just means this particular material is more difficult and working through the difficulty can be a great source of personal confidence.
Often when students encounter math to be increasingly difficult they start identifying with not being "good at math" any longer, but this couldn't be farther from the truth. The earlier the intervention, the better.
Once students think of themselves as struggling math learners, it's much harder to reach them, even if it is within their capability.