What is the difference between AP and IB classes?

Although both Advanced Placement (AP) and International Baccalaureate (IB) classes give students the opportunity to take college-level courses in high school, the structure of the programs and how colleges treat the work done in those courses differ.
Students can take a single AP class in high school and take its accompanying test to see if, based on how well they do, they can qualify for college credit. Likewise, an individual IB class can be taken, but IB also exists as a two-year program. Although some schools offer pre-IB classes leading up to the final two years of high school, IB classes officially start in a student's junior year of high school. While all AP classes are a year long, only standard-level IB classes are. So-called "higher-level" classes last two years, and students seeking a full IB diploma must take at least three higher-level IB classes. Additionally, they must fulfill a community service requirement, write an extended essay, and take a class on the theory of knowledge.
AP exams are scored between 1 and 5, with 5 being the best score possible. On IB tests, students are scored between 1 and 7; in this case, 7 is the best score possible. Colleges will often give credit or allow students to test out of classes if they score at least a 3 on AP tests or 5 on IB tests, although some universities will only recognize higher scores. Currently, most colleges offer credit for both AP and IB classes, but some only offer credit for AP test scores, as AP is far more common than IB. Students can take AP tests without taking its accompanying class, but IB tests can only be taken by students who are in the related IB course. As a result, some students take IB courses and then take AP tests. AP tests can also be taken by any high school student, whereas IB exams can only be taken in the junior and senior years of high school, as that is when IB classes are available.