Within the classroom model there are various types of classes. The most common type, and the one for which this manual in primarily designed, is the situation in which there is more than one class and the students are divided into classes according to proficiency levels. In this kind of class, even though the students are grouped according to proficiency, there will always be some students who are more advanced than others. In addition to these differences that exist at the beginning of the class, the program will usually have a policy called "open enrollment." This means that students can continue to enroll after the class begins. This makes it necessary to play the instruction so that lessons are as nonsequential as possible, that is, each lesson can be taught independently of the previous ones. While this is not entirely possible, it is desirable to have lessons that can accommodate new students as well as those who have attended previous lessons.
The differences in students mean that the teacher will need to plan activities that allow for different levels of performance in each thing being taught. The best way to do this is to break the class frequently into small groups for part of the class time and work with each group on their level. This is particularly true if the class has students who do not read in their native language.