Student syndrome refers to the phenomenon that many people will start to fully apply themselves to a task just at the last possible moment before a deadline. This leads to wasting any buffers built into individual task duration estimates. [1]
It was noted by Eliyahu M. Goldratt in his novel-style book about Critical Chain, titled Critical Chain.
The student syndrome is a form of procrastination, but it usually includes more of a plan and sincerely good intentions. For example, if a student or group of students goes to a professor and asks for an extension to a deadline they will usually defend their request by noting how much better their project will be given more time to work on it; they request this with all the right intentions. In reality most students will have other tasks or events place a demand on the time they fully intended to commit to improving their paper or project. In the end they will often end up close to the same situation they started with: wishing they had more time as the new delayed deadline approaches. The student syndrome is defended by a layman's understanding of the functioning of the human memory, most notably the concept that a person's short-term memory fades over time, and thus studying at the last possible moment (cramming) will allow more to be remembered during the exam, even though cramming damages long-term retention and is significantly inferior to a spaced presentation (which exploits the spacing effect).
This same behaviour is seen in businesses; in project and task estimating, a time- or resource-buffer is applied to the task to allow for overrun or other scheduling problems. However, with Student syndrome, the latest possible start of tasks in which the buffer for any given task is wasted beforehand, rather than kept in reserve.