Most retailers reported better than expected sales gains in September as shoppers scooped up back-to-school items and apparel. The one weak spot in the month was discount store retailers. Wal-Mart Stores Inc., BJ’s Wholesale Club Inc. and Costco Wholesale Corp. all reported disappointing sales for the month. The Children’s Place Retail Stores, Nordstrom Inc. and Kohl’s Corp. were among the leaders, reporting September sales rose 20 percent, 13.4 percent and 16.3 percent respectively. According to the International Council of Shopping Centers-UBS index, retail sales for all sectors rose 3.8 percent for the month. Excluding Wal-Mart, the index revealed a 6 percent increase for the retail sector. Experts attributed the increases to cooler September temperatures and falling gas prices. At Wal-Mart, however, same store sales rose just 1.3 percent, compared to the 2.1 percent growth analysts had predicted. BJ’s same store sales declined 0.9 percent, versus an expected gain of 2.3 percent and Costco sales rose 4 percent, compared to a 5 percent prediction from The Street.