M.C.
I used to work in an IB school, and plan on sending DD to one when she starts kindergarten. Simply put, the International Baccalaureate system in internationally recognized and transferable--so that, for instance, if you move to London, or Bucharest, or your kid decides to go to university in Australia, the curriculum and diplomas will be recognized. As you may (or may not) know, many countries have significantly higher standards for high school graduation/college admittance than the US does. For example, in many European countries, college-bound students go to high school until they are 19, doing what is there considered high school work until then (with none of this AP, concurrent enrollment, CLEP business--it actually takes you until you are 19 to fulfill all of their high school requirements). In Switzerland, where I worked in the IB school, an American Associate's degree is considered to be the equivalent of the Swiss Maturite (the HS diploma required for admission to a public university). This is another way of saying, if you want to go to college in Geneva, a standard American high school diploma won't get you in.
The result of all of this is that, in order for an IB school's curriculum to be recognized internationally, it has to be significantly more rigorous than a standard American public school. In the US, most IB charter schools are required to accept students regardless of ability--so while some people think that IB schools are geared towards gifted and talented kids, this is not necessarily so. However, you should expect high standards and expectations for all kids--as I would tell my students, I will work with you as much as you need, we will get you extra tutoring if necessary, but you are required to "get" this material and meet these standards. If you choose to send your kid to an IB school, you should expect them to learn a lot, and work a lot (particularly in the high school years). The academics are, in my view, excellent, and IB diplomas are looked at very favorably by most colleges. For example, I went to an Ivy League university that did not accept AP credit, but WOULD give college credit for an IB diploma, letting you start as a sophomore. Obviously, this is a long way off from elementary school, but the standards start from the beginning. The IB school DD will go to starts the first foreign language (Spanish or Mandarin) in kindergarten, the second foreign language (whichever you didn't pick the first time) in 3rd grade.
I would say whether or not you choose to go with an IB program depends on your priorities. If you want strong academics, and are willing to be involved with your kid's education (helping with homework, etc.), then it can be great. It does take some commitment, though, and might not be best for every family. Feel free to PM me if you have more questions.