Recently, my grandson started kindergarten. He loved the first day of school. Even so, he did not want to go back the second day. He was worried because the teacher told them they would have a fire drill the next day. Because he had experienced a fire at his home, he was afraid. He did not understand what a "drill" was. Therefore, he was anxious.
This anxiety is very similar for children who struggle in school. If they do not understand what is going to be happening, they get anxious. Often, they have experienced failure before, and they think they will fail again. Telling them, "You'll do okay," does not help. They need to know what to expect so they can be mentally prepared for it.
For example, my students often ask, "What is going to be on the test?" At first, I think they are really asking me to tell them what is on the test. But, generally, they just want to know what the test will be like. If I say, "It is on magnetism. There will be a matching vocabulary section at the beginning. After that I will allow you to choose 6 out of 8 short answer questions. Then there will be three long answer questions, and you get to pick two of them." That usually satisfies them. They know what to expect.
If your child seems anxious about something, try to figure out what they really need to know in order to be better informed about the upcoming events. It is often fear of the unknown that worries them. This can be about a new teacher, a new school, a change in transportation arrangements, or any number of things that happen when children go to school.
Best wishes for a happy start to the school year. We started off by closing the first five days because of Hurricane Irene! Talking about anxiety.....