Retailers, hoping to boost sales, started bringing out back-to-school merchandise in June, just as the last school bells were ringing before summer vacation. The back-to-school shopping season usually lasts from mid-July until September, but this year 52 percent of consumers had already begun shopping for the coming school year by mid-July, up from 33 percent in 2007, according to a report from Citigroup Global Markets Inc., the Chicago Tribune reports.