Having recently moved to Germany with children, I was asked to share my experience...
I decided to move to Germany when my youngest was a freshman during the second half of the year. I can only speak to "high school"... If you were moving a younger student, I would refer to the article I've linked below to see where your student falls in the current system if you want to go in the traditional German system.
The #1 biggest factor is the language as Beppi mentioned. If you plan to move to Germany and put your child in the traditional German school system, start language tutoring as soon as you make the decision. Learning the language is one thing, but studying in a foreign language is a totally different ballgame. It will be a situation where your child will not understand everything being said on a semi-daily basis and will be learning new vocabulary every day. I know this because my 19 year old attended language school as soon as we moved here. He got to the recommended B1 level as per the Studienkollege and started University. He's studying in German and it is no joke. He graduated in the states top 5% of his class with about 15 hours of college credits in the form of AP classes. He's a sharp kid. He is determined to make it work and he is succeeding, but he definitely has his days of wanting to throw the towel in.
In America, a student enters high school, carries out the required 4 years of high school and receives a high school diploma. In Germany, after the "10th" grade, a student may enter an apprenticeship or attend a trade school. Alternatively, they may continue their schooling and obtain the Arbitur which will have prepared them for University.Â
There are two degree paths for a student in Germany. The Arbitur and International Baccalaureate (IB)... These must be understood in order to assess which is the right path for your child and the best way to transition them.
The German system can be hard to grasp coming from another country. This article sums it up perfectly and you can see how things are broken down...
I moved my son at the last point, I believe, you could successfully move an American high schooler and continue the path he was on, which was as soon as he had finished the 9th grade in the states. Because of the differences in the school system, his age and where he was in the process, I decided to send him to an International HS to obtain the IB. At his school, one can obtain the IB or the Arbitur. There are about 50% German students and 50% international students. As mentioned, these schools aren't cheap. It was a sacrifice for sure. But it was important for me that he be the one that transitioned the easiest.
School schedules run more like an American college. He has certain subjects on certain days of the week - not like math every day of the week at a scheduled time. The last two years of the IB run more like the last two years of a Bachelor's degree in the States. The curriculum is intense. It requires a lot of work and the students really need to stay on top of their work or they will quickly fall behind. My son felt behind in chemistry, physics and math when he started. The students at his school had been studying these subjects for several years already and were at a much higher math level. He's put in a lot of hard work and feels comfortable now. Prior to our move, I bought him several books on higher level math that proved to be excellent resources for him. He glanced, briefly of course, before we moved but I know he's used them as a guide when he gets stuck here.
This being said, my son transitioned as well as to be expected when moving to a new country. His school is English speaking and he quickly made friends. With the year almost over, he has a pack of friends from all over the world and loves it. The teachers at his school recognize and understand there is a transition time with the students when they first arrive. They may have cut him a little slack at first but have been great at starting to push him when he needs it. With the school having such a heavy German influence, he has enjoyed acclimating into German culture. He gets this exposure from his German friends at school; and since I'm married to a German, we acclimate to the culture as a family.
One of my biggest mistakes was going back to visit the states too soon. I realize now I should have waited at least 6 months before I went back. He came back to Germany pretty homesick. He withdrew from his friends at his new school and became quiet at home. We talked and talked through it. We pushed through it and he soon was back in his groove as he understood that we will always be back home to visit our family and friends.
That about sums up our experience. My #1 advice would be to start language tutoring as soon as you decide to move. With everything that goes into an international move, once you get here, you'll be getting so many things squared away. Once less headache is having the ability to communicate on at least a basic level. Once you decide the area you are moving, call the schools. I came to Germany and did several campus visits to decide which school would be right for my son. Talk to the educators. Get a feel for how they handle °µÍø½ûÇø students. What are their expectations? What are YOUR expectations? Who's the best team to help your child transition? AND, Google searches are magic at helping you find what's available in your potential areas...
I'm sure those who live in Germany such as Beppi and Tom can clarify the German school system or anything I may have botched on that end... 