According to the National Retail Federation's survey of 6,285 shoppers, the average family with children grades kindergarten through grade 12 had completed 49.9 percent of their back-to-school shopping as of Aug. 12. Coupon site Retailmenot, which works with 50,000 retailers online and in store, says the number of back-to-school coupons spiked nearly 60 percent in mid-July through mid-August, compared with last year. Shoppers have been able to get prices of items matched at stores like Best Buy and Target if they see it higher at rivals. The online tool allows customers to compare Walmart's advertised prices on thousands of products with those of some competitors. If a lower price is found elsewhere, Walmart refunds the difference in the form of a store credit. Retailmenot.com has an app that uses GPS at 15,000 shopping centers to push coupons to shoppers' smartphones. Parents and kids can turn to online consignment sites, to pick up gently used trendy items. [...] ThredUp.com has a "back-to-school" tab where parents can buy Polo Ralph Lauren short-sleeve shirts for $4.99 and DKNY jumpers for $9.99.