Hi!
So I really want to study abroad during my junior year in high school at a British boarding school but I don’t know how to execute it. I would preferably like it to be cost-free / have a full scholarship. Do you guys have any ideas on how to make this happen?
Thanks 
There are boarding schools that have programs abroad. Miss Porters used to have a type of study abroad or exchange program during the winter session or the January weeks that includes a BS in GB (think Kent) - believe it’s paid for either for 11th or 12th grade students. There is one abroad trip that is fully funded. You can call their AO to find out.
Did you check out Rotary International for high school study-abroad programs that are free?
St. Paul’s School has an agreement with Eton College in England. I believe that Eton is an all boys / all male school. SPS has very generous financial aid including 100% grant aid for families earning $125,00 or less per year.
If you are open to attending a boarding school in Wales, consider applying for United World Colleges (UWC). They are a network of 17 boarding schools around the world. Students are selected by their home country to attend one of the UWC schools for two years and complete an IB program. Most students attend either junior & senior year or senior year plus a post-grad year. Depending on where you currently live, your country committee might have funds to subsidize the cost in its entirety.
See if your school participates in the Round Square program, where boarding schools around the world do student exchanges.
Also see if your school has someone in charge of International programs. Different schools have different rules about who can go, and where they can go.
Round Square is a great program. My kid did it during the last quarter of her Sophomore year. It was a great experience and helped her in her language. There is a downside though in that the course material will likely not line up very well in all of the classes. We had to have our kid tutored in math and science over the summer to catch up on what she missed so that she would not be behind when she returned in the fall. And if sports are important, missing a year/season of an important sport can mean a set back if, for example, you aspire to playing a sport at a high level. And while many kids do take part of their junior year abroad, it can be tricky since it’s an important year leading into college selection.
Look into the ESU (English speaking union) program. It’s a scholarship exchange program to a British boarding school for a year after graduation. I participated and took A levels (like AP courses) to earn college credit.
Westover School (all girls, boarding school in CT), has programs for study abroad that last from several weeks to a full term. They exchange with a girls’ school in England. No extra tuition cost, just transportation and spending money. Their program in Jordan even has airfare cost covered by the Jordanian royal family, as one of their daughters is a Westover alum.