I'm a US Citizen schooling in another country. Do I need TOEFl?

Yes, you have to take the TOEFL exam if all your education was from the country whose official language is not English.

However, if you are simply an ex-pat who temporarily moved outside of the US because of your parent's job, and you have high SAT, ACT, or SAT Subject 2 scores or high AP scores, I would ask the college you are applying to first prior to making any assumptions. 99% you should be good to go.

Good luck.

I'm also a US citizen studying in another country and I've also not done very well on the English section of the SAT.

Just because you live in a country that is not the same as your citizenship, that does not mean that you are an international student. If you study in a country where English is one of the languages then you will be fine and you won't need to take the TOEFL. Also, keep in mind that your standardized test scores would not and should not determine whether you need to take the TOEFL. Like @Quique suggested, you may want to check through the universities that you are interested in to see their requirements of tests like the TOEFL.

Hope this helps.

Is your primary language English? Are the classes you take in English? If so, you're probably not going to have to take the TOEFL. Keep in mind the average SAT score is about 1000, or a 500 on each section, so a 600 in English is not going to raise any alarm bells for colleges. In fact, I don't think your SAT score has any bearing on if you would need to take the TOEFL.

Having said that, I would still recommend that you take a look at any of the colleges you're interested in applying at to double check their TOEFL policy. The individual policies may vary from school to school and I would hate if you missed a requirement somewhere.

Most universities will require you to take the TOEFL, but it depends on how many years you have been living abroad, if your first language is English, etc. Some colleges will probably ask for it, but each one is different. I'd look through their websites to see their English requirements for international students.