It is unavoidable that at some point your child will probably have an issue at school that you may need to step in and help resolve. One of the main issues that happens at school is that the child starts to get bullied or that they are having difficulties with friends. This is very common throughout their school life and when they are younger you may need to help them sort it out. If it is just normal falling out with friends then it is best to teach them how to deal with it themselves rather than stepping in every time. If it is more complicated and you feel they are being bullied then you may want to go in and speak to the school.
It may be that you need to speak to their teacher first and if you are not happy with the way in which it is being dealt with you could then go and speak to the head teacher. Teachers usually have a way in which they need to deal with problems that are reported to them and often take bullying very seriously. Teaching your child skills on how to deal with issues will not only help them at school but throughout their life.