Students who are socially promoted have not demonstrated adequate understanding of academic content. While for some this failure to make the grade may be due to laziness or absence, for others it is due to a failure to understand the concepts presented. If a student who did not understand the concepts in one grade is promoted to a higher, he will likely struggle even more acutely in this more challenging academic class.
Many proponents of social promotion argue that the practice sends the wrong message. If a student fails to earn passing marks but is passed on anyway, he may begin to see earning passing scores as an optional thing. After a year or two or social promotion, this student may begin to feel that it doesn't matter if he does the work, as he will just be promoted anyway.
Students who are allowed to fail but then are promoted socially may develop learned helplessness. Learned helplessness is the condition in which a student doesn't feel that he is capable of achieving a goal and, as a result, stops trying. If a student sees that his teachers seem accepting of his failing, he may feel that they are accepting because they don't actually think that he can do it and, as a result, he may stop making the effort.
When a student fails an academic grade, there is often a larger issue at the core. If the school simply socially promotes the child without exploring what caused him to fail in the first place, this issue may never be fully addressed, leading to the perpetuation of the problem instead of addressing the challenge that led to the failure to begin with.