Research studies produce different results as to the extent of the loss, however they all appear to agree that the loss in learning varies across age and grade, subject matter, and family income and socioeconomic status. In 2017, one review of the research in the U.S.A. concluded that a) "on average" students lost one month of learning over the summer months, b) losses were higher for math as compared to reading, c) higher grade levels experienced more loss, d) the income-learning gap was especially significant because middle-class students tended to show an improvement in reading skills during the summer while lower-income students tended to experience a loss in reading skills (there was not a similar gap with respect to math), and e) there was no difference by gender or race in either subject.