Math
In the real everyday world, a pilot will directly use simple math only. Add, subtract, multiply and divide. And the math skills of many pilots are interesting to say the least. Based on the trip documents I have audited in the past couple of months, I have found several pilots who when they add 2 + 2 come up with every number but 4. It is not because they are dumb, but when people get in a hurry, it is easy to make a mistake and usually it is little things like forgetting to carry the 1, etc. So I active encourage people to use calculators. I have also found that after you become familiar with an aircraft and the company's system that errors will start jumping out at you.
The rules of thumb are math based but are in a simple form that make them easy to remember and use. Remember you are also busy trying the keep the shiney side up.
Back when I was instructing on a regular basis, I had a couple of high school math teachers that insisted on using trig rather than the E6B (I know, I am dating myself) and could not understand why their answers were not right. The tests are designed around the E6B.
As for what to study in school, the guidence councelors will alway insist you be heavy on the math and sciences, but there is no major requirement in those areas, except for the military. It is my personal opinion you will need the following:
English. All aviation activities are in English.
Business writing. Resumes and business letter.
Creative writing. For all those trip reports and expense reports you will write in the future.
Computer science. Most of the new aircraft are computer operated and you will also use computers in your daily opeations and for training, so you need to get comfortable with them.
Geogrophy. And I mean the world not just the US. You need to know where you are going. There are a lot of people who don't understand that there are several cities and towns in the US called Atlanta. And so on.
Foreign Laungage. Not a major issue, but most colleges require it. For international operations it helps. I would suggest Spanish, but it's just me. It does make it easier dealing on international flight if you can even say a few words in their tongue. Hello, Please, Thank you, bathroom, beer, etc.
At least one mechanical shop class. I have found over the years the pilots who have at least a working knowledge of how things work and how they are put together, do much better in ground school. It is also handy to know what end to the screwdriver and wrench to use.
A class or two in salesmanship and marketing is also handy. After all you will have to sell yourself when you start looking for a job.
Science in that the industry we are in evolded from and revolves around science. And you need to basic sciences. Biology, chemisty, physics, etc.
While many of the classes you take in High School will prepare you to become a well round, useful member of society, over the years, I have come to realize that the about classes I took were some of the most useful in my career.
Good luck