Social loafing is a phenomenon where people who are grouped do less work because they become co-dependent of the other members of the group to do the work for them. This is a situation that occurs often when groups are made hastily without taking into consideration individual strengths.
A common occurrence of social loafing happens in college settings. A professor might assign different projects and quickly form groups of students to complete them without considering what each student can really offer the group individually.
As it often happens, college courses are populated by students of all walks of life and of different levels; for example, a freshman might be taking a course with a sophomore after having qualified through advanced placement, etc. In groups so heterogeneous it is essential to identify traits that might match students for productive group work. Unfortunately, this precaution is seldom taken at the college level and professors assume that students know how to group themselves. The problem then occurs that a student who is too busy might rely on a student who is not that occupied and will rest upon that to avoid doing extra work.
There is also the case of the over-achiever who wants to do all the work in the group in order to claim all the credit when, in reality, the other members also had all the intention to work together. This is basically what social loafing is about within an academic setting.