ESL is often taught as a pull-out class where students are taught primarily in English speaking classes and leave for part of the day or week to learn English.

In their ESL pullout groups, students have access to a teacher who can help them with problems they may be having understanding their regular course content, and they also receive instruction in English language.

A major benefit of ESL programs is that they generally are taught entirely in English, allowing groups of students with a variety of native languages.
These programs also allow students to remain in the mainstream classroom most of the time so that they can keep up with their classmates. At the same time, these students are removed from their regular classrooms, leaving them with the sometimes difficult task of catching up on material covered while they were in ESL, and there is the risk of alienating these students or creating a stigma when these students are removed from the classroom, though the risk of stigma can be reduced significantly if it is dealt with by the classroom teacher.
These risks are much less when ESL is used at the High School level. At this point students miss out on an elective class, but they are not missing class time for which they will be tested, and they are not removed from the class in front of their peers.