You need to find out what the best schools are in the metropolitan area you will be living in, and then find somewhere to live within the School District for those schools (elementary, middle, and high schools will have different Districts). The School District is the administrative body running the schools. In a generally affluent area, there will be good schools.
For high school, please be aware that basic state or District graduation requirements (expressed in terms of credits, often with one semester - half a year - equaling a credit) will fall well short of what universities expect to see on a student transcript.
For instance, a state may require that students do 4 semesters of mathematics, whereas universities will be looking for 4 years (8 semesters) and the selective universities will want a student to have done at least AB Calculus (beginning calculus at AP level) by their final year of HS. Same goes for other subjects - universities in general want to see honours level courses, preferably AP courses (in general, freshman college level) and more years of core subjects than the District or state accepts as evidence of completing the course of studies.
You will find if you want your child to follow an honours track and apply to good universities that they will need to do very much a traditional academically oriented English, MFL, Math, Humanities/History, Science and Elective subject track all through high school, with little room for classes like broadcasting or automotive tech or fashion design, etc. There may be scope for credits in editing a school publication under the heading 'English', and this is a good thing for university applications.
If you think you need to prepare academically, then focus on maths and science. Quite often, high schools will assign a level in classes in both maths and science based on the score in a standardised maths test administered in 8th grade (final year of middle school). Maths and science are pegged together. You can generally look on your school website to find the level of maths expected.
Your child will need to get up to speed in American history too from exploration by Europeans of the New World through the American Revolution, establishment of the constitution, the system of government, civil war, westward expansion, gilded age, ww1, depression, ww2, aftermath, with economy, society, cultural topics thrown in.
YYY - GPA system means you do your best work consistently from day 1.
Depending on the size of the school, your student may find him or herself in classes with students from the other years. My own DCs had art classes with students aged 14-18, from different years, and same for other classes too, especially maths, where students were all on individual tracks. In DD2's final year there were two freshmen taking BC calculus. DD4 did World History as a sophomore, one of three in her particular class. She will do AP US History next year and probably AP Psychology in her senior year. There may be students younger or older than her in her APUSH class. It's not like the UK where you stay with the same cohort advancing through each year of school. Schools are obliged to cater for the needs of all students within their walls, and if there are 14 year olds able to do university level engineering courses then that is what they get, in a School District that can afford to provide that level of educational resources.
Your student may do daily PE, may have an obligatory study period daily, may have lunch at 10am depending on scheduling and how many students eat lunch, may have a closed campus rule...
They will have a locker, will probably have a vast number of extra curricular activities to choose from - sports to arts, music, volunteering. Encourage involvement.
What goes wrt clothing depends on the culture of the area you find yourself living in. Kids around here generally don't mind what they wear or what others wear. Middle schoolers can be a bit more conscious of themselves and others though.
Not having a uniform is a huge plus imo.
My advice wrt schools is,m once you have found a good one and found somewhere to live within the District (double check this) - look up the school academic catalogue online, and read it carefully. Read school handbooks, and District policies on academics, sports, and discipline. Get familiar with the GPA system.