How will I be reviewed in college applications?

I am a 17 year old american student. I completed my freshman and sophomore year in an american high school with a less than average GPA. I was not much of a studious individual and was not too proud of my direction academically. Frustrated with myself and wanting change and something to be proud of and accomplish, I decided to study abroad in France for my junior year. It was not to party, have a year off or to behave like a wild exchange student. I wanted to learn a lot in my exchange year and encourage myself to have an academic challenge. It worked hard learning the language and now I get decent and reasonable grades for an exchange student.

Next year, I was meant to return to the United States and continue my regular american AP system. One day, I came across the IB Diploma through internet research. I was immediately inspired and I wanted to change to this school system for an even greater academic challenge. I am enrolled in an IB Boarding School in France for 2015-2017.

I plan on having a fresh start, completely putting behind my old self from freshman&sophomore year. I am a changed student and I plan on working really hard during my 2 IB Years.

I am not sure what grades I will be showing to colleges. American colleges look at the 4 years of high school (generally)

With my 2 years in american school(freshman&sophomore) ,1 year in France(Junior) and the 2 years enrolled in the IB Diploma, I would have 5 years of high school in total. Which school years get counted? Will colleges only look at my IB years? Will colleges consider both my GPA and IB? If I had a mediocre GPA in freshman& sophomore year but then showed huge improvement in my IB grades and got a good SAT/ACT score, does that make any significance for my college application?

I honestly have no idea, but one possibility is that you failed a year and had to repeat it.

You will be looked at as an American student who did two yrs school in the US, had a year off and did 2 yrs school
overseas, the IB diploma is common enough in the USA, admissions know how it works. The time button doesn’t restart for the IBD, as you know, only your first year at the new school will be reflected in your application anyway, are you doing the whole IBD in French, or at least the bilingual dip? Or just plain old English?

I will be doing the IBD in English with French as my second langue, a bilingual diploma.
Students with an IB Diploma have different registration criteria for colleges no? So instead of colleges looking at 4 years, they will be looking at my 2 years spent in IB?

What do you mean by registration criteria? Do you mean eligibility, sure they might tie your admission to a score.
No they won’t look at just 2 yrs, they will look at your whole high school. Many kids (thousands maybe) take the IBD in the USA, it is not some kind of novel product. You are an American, not a European, you have 2 yrs of US high school, just because you want a fresh start, that doesn’t erase that period. And again, you are applying at the end of jr year, you will only have 1 yr of the IBD reflected in your application. You haven’t started the IB yet, grading, projected score, rigour etc are a complete unknown as yet. SAT? ACT? PSAT? You might want some raw stats.