Pre-IB and IB Art classes are to prepare students to take the IB Exams for art. Some information about introductory levels can be found here. 
 
Students can examine at IB standard level (IBSL) and IB higher level (IBHL).  IBHL earns more points towards your IB diploma.  Only juniors and seniors are allowed to examine. 
 
IB exams contain 3 sections:
 
Comparative Study:  20%
Students do an extended project comparing 3 artworks.
Process Portfolio:  40%
Students share their journals where they talk about art and artists, explore new media, record and reflect on their process and so on.
Student Exhibition: 40%
Students create a body of work and curate its exhibition.
 
Because of this focus on process and criticism in addition to art production student assignments differ somewhat from  AP classes and while the development of hand skills is important it is not the only thing that allows students to make high scores.  Writing and thinking about art are also factored into student scores.  Students who wish to take IB should be comfortable with writing.  IB students spend a good deal of time not just making art, but talking and thinking deeply about it and recording their progress.

More detailed information can be found at the IB Visual Art website.  I also uploaded a brief overview that goes over each section of the test in a bit more detail here.