Every year, thousands of college freshmen choose a particular major field of study, and the following year thousands of college sophomores change their minds abruptly. This sudden switch is often triggered by an especially challenging but required course known as a weeder class. A weeder class can either be an academically difficult course, such as organic chemistry, or an average course presented by a demanding instructor, such as a freshman English composition class taught by the chair of the English department.

A weeder class is designed to thin the student herd, especially in fields where advanced courses are notoriously demanding. Pre-med students, for example, are generally required to enroll in higher level chemistry courses, such as organic chemistry and biology. Organic chemistry is a very difficult course under the best of circumstances, so a number of students may drop out or switch to less demanding majors based on the difficulty of a weeder class.

There are certain courses which are not intentionally designed to be weeder classes, but they still serve the same purpose. A freshman or sophomore level English course, for instance, may not sound challenging at first, but the instructor could make it much more difficult by assigning lengthy research papers, adding additional reading requirements or grading declared English majors more strictly than the rest of the class. The point of such a weeder class would be to provide a sample of what to expect in upper level or graduate courses.

A weeder class is the polar opposite of the so-called Mickey Mouse, crip or clap for credit classes. While these rudimentary courses are known for their easy workloads and generous grading systems, a true weeder class often gains a similar notoriety for having a brutal workload and strict grading guidelines. A good academic adviser should be able to guide a student through the minefield of Mickey Mouse and weeder classes in order to prevent an academic meltdown. If a student enrolls in too many weeder classes at one time, he or she may become too discouraged to continue in a potentially rewarding field of study.