Amazon is schooling the retail industry on how to turn "1+1" into science. Hopefully, retailers are taking notes. Prime Day has pushed up the shopping season by nearly a month. More important: The report finds that Prime Day back-to-school shoppers spend 17% more at brick-and-mortar stores and 16% more at combined brick-and-click stores, compared with shoppers who don’t participate in the event. A major contributor to the earlier kickoff of the back-to-school shopping season is that other retailers, such as Target, have responded to Prime Day with their own earlier promotions. In addition to higher sales, however, several studies reveal that how shoppers buy their clothes, backpacks and dorm-room furniture is shifting in important ways that could predict the course of school shopping in years to come.