Also known as the Summer Slide, this refers to the tendency for students to lose some achievement gains when they are out of school during summer. The concept has its origin in research studies arguing that the educational level of students, when schools opened after summer, was lower than at the beginning of summer. Such learning loss is said to be equivalent to about one to two months of learning and found to be higher in the case of subjects such as mathematics. In some cases, it can also cause teachers to spend a significant time after summer trying to teach lessons from the previous academic year.