• by Sarah Mahoney  @mahoney_sarah, September 18, 2012

As merchants sift through their back-to-school receipts, it looks like the season’s two best sellers were social and mobile sales.

IBM’s Benchmark reports that social sales, or online sales that happen as a result of a referral from a social media site, accounted for 1.6% of July sales, a jump of 25% from the prior year, and 2.2% of all August sales, a 69.7% increase. M-commerce increased by 15.7% in July, and 15.4% in August.

Overall, online sales gained 11% in July, then slowed to a 3.9% advance in August.

Surprisingly, though, while consumers may have been spending up a storm during the back-to-school season, it wasn’t on school-related items. In fact, home goods had the biggest growth, with purchases climbing 30% in July and 25% in August.

 The IBM Benchmark study also uncovered impressive growth in department stores, where online sales grew 22.1% in July and 28.7% in August, with mobile sales in that channel gaining 19.2% and 18.9%, respectively.

Gains in apparel were more subdued, with online sales advancing 9.2% in July and 9.8% in August, with m-commerce climbing 15.1% and 16.4%.  Social referrals were strongest in this sector, up 113% in the two-month period, more than in any other industry.

And in electronics, online sales managed to gain 6.3% in July, but then fell 0.9% in August. Mobile sales made up just 5.7% of those transactions in July, and stayed at that level in August.

“Back-to-school season is proving to be a trigger event that spans across categories beyond just notebooks and backpacks,” notes Jill Puleri, Global Retail Leader, IBM, in its release. “Retailers that are cashing in are those who understand how this trigger drives sales for home furnishings, as well as for apparel, and can target their inventory levels and promotions accordingly. This year's winners were companies that successfully connected consumers with the right products, at the right price, and through the right medium–whether in a store, a mobile device or through popular social media channels."