For students: No previous folding experience is required to take classes rated simple.
For teachers: The models should have mountain and valley folds only, be relatively forgiving of small errors, and have reference points for everything. Even the most basic of maneuvers and techniques should be explained, i.e., say 'fold bottom edge to top edge, which is a book fold,' rather than 'fold a book fold.'
Examples: Swan, magazine cover box, jumping frog, sailboat
For students: You should have some familiarity with origami terminology and materials.
For teachers: You can assume your students have folded before, but may not know terminology. The models should be primarily mountain/valley only but with the addition of inside/outside reverse folds and squashes.
Examples: Waterbomb, star basket, tulip/leaf & stem
For students: All of the above, plus you should know how to fold a bird base from memory, and be good at inside reverse folds, outside reverse folds, and basic sink folds.
For teachers: You can assume that your students know basic terminology, but be prepared to reinforce. For example, you might say something like: 'fold a colored preliminary base, that is, colored side up fold two diagonal folds, then white side up fold two book folds.'
Examples: Flapping bird, crane
For students: All of the above, plus you should be comfortable folding double rabbit ears, crimps, double sinks, closed sinks, and stretching a base.
For teachers: Before the class starts, explain what advanced maneuvers are included in the model, such as a closed sink, and give the students the opportunity to change to another, simpler class. Assume that the students are familiar with these maneuvers, but explain them as you go. For example, don't just say 'then fold a double rabbit ear,' but rather describe the maneuver step-by-step.
Examples: Jack-in-the-Box, Montroll 3-star models
For students: All of the above, plus you should be an experienced folder, be comfortable folding from diagrams, and be able to follow intricate sequences of precise moves.
Complex models might have "collapse" moves, where many creases come together at once. They are also commonly very sensitive to folding errors, so that if you do not fold precisely early on you won't be able to complete the model.
For teachers: Before the class starts, explain what will be expected in the class, such as folding something precisely into a grid of 64th's, and give the students the opportunity to change to another, simpler class. You should not have to explain any standard maneuvers, and should be able to state an objective and let the class proceed, such as 'please fold your paper into a grid of 64th's.' But be very aware of your students' progress, because a simple error early in the folding progression may result in inability to complete the model.
Examples: As defined by the creator of the model
For the student: Super Complex models are the catch-all for anything harder than the preceding. A Super Complex model might contain: Multiple nested sinks, extensive precreasing followed by collapses, and collapses with ten or more creases coming together at once.
For the teacher: Most Super Complex classes are limited, either specifically by you, or by natural selection. Don't be afraid to question each student individually as to the most complex model they've ever folded, and to gently suggest that the class might be too difficult for them. In a class rated Super Complex, you should not feel obliged to help a student who falls hopelessly behind.
Examples: As defined by the creator of the model, and especially anything that takes more than 3 hours