One thing to consider if you are thinking about doing your senior year of high school as a study abroad is that you will need to do all of the college application stuff while in another country. Teacher letters of recommendation, writing application essays, requesting copies of transcripts. You should also consider any standardized testing…if you find that you need or want to retake the SAT or ACT to try for a higher score in the 1st part of senior year, then you’ll have to navigate that while overseas.
Honestly, if you’re really serious about pursuing a career in social work, I do not think that you should spend senior year of HS abroad. I think you should stay at home for senior year…do some dual enrollment classes like you mentioned…maybe come up with an independent study senior project through your HS, something that involves social work or sociology.
Do study abroad in college.