Updated from 9:06 a.m. EDT

SAN FRANCISCO -- Back-to-school shopping had consumers flocking back to stores in August, helping retailers make up for some of the sluggishness they had been experiencing all summer.

The nation's big chain stores on Thursday reported stronger-than-expected sales for the month, with many of them touting strong back-to-school selling. But while the results exceeded expectations on Wall Street, they represent only a one-month snapshot of an industry that still is plagued by concerns that shoppers may be hit by housing and credit-related troubles.

Retailers collectively reported a 3.1% increase in August same-store sales, or sales at stores open at least a year. That topped analysts' expectations for a 2.5% climb, according to Thomson Financial. Still, the growth was below last year's 3.9% rise in August.

Industry giant

Wal-Mart

(WMT) - Get Report

, which analysts thought would be a drag on the industry, helped to boost the results with its better-than-expected sales. Excluding Wal-Mart, same-store sales still came in at 3.1%, less than the 3.3% increase Wall Street was expecting.

Of 45 retailers reporting August results, 67% beat analysts' same-store sales expectation, while 33% missed estimates, according to Thomson.

Mike Niemira, chief economist for the International Council of Shopping Centers, says that although August showed an improvement over July, when same-store sales rose a collective 2.9%, the difference is only slight.

"It's not so dramatic a change that you say, 'Wow, look at this, we're home free here,'" Niemira says.

The same conditions that have been a drag on retailers since February, such as the housing slump, still apply today, he says. Monthly same-stores sales have consistently been down about a percentage point vs. last year, a pattern that continued in August.

Overall, back-to-school selling was expected to rise over last year, since many shoppers consider the purchases necessary, rather than discretionary, spending. The strength in August relative to June and July indicates that shoppers had been waiting until late in the summer to make their purchases for the season.

In addition, August benefited from a shift in a tax-free sales week as well as late start dates for school in Texas and Florida.

"That's not the story in September and it could very well be a fleeting part of the picture," Niemira says. "The best we can hope for is that it doesn't get worse and that it gets steady."

The world's biggest retailer, Wal-Mart, posted a 3.1% rise in same-store sales for August. The world's largest retailer had projected a 1% to 2% climb; analysts had forecast a 1.5% increase.

Wal-Mart said back-to-school categories drove results, with particular strength in sales of electronics, school supplies and children's apparel. Back-to-college items such as bedding, bath towels and storage items helped boost sales in the domestics category.

For the September sales period, Wal-Mart expects same-store sales to rise 1% to 3%.

At rival

Target

(TGT) - Get Report

, same-store sales jumped 6.1% in August, compared with its forecast for 4% to 6% growth. Analysts projected a 5% rise.

Department-store giant

Macy's

(M) - Get Report

, which has been an underperformer of late, posted a 2.4% climb in same-store sales, beating analysts' forecast for 0.3% growth. The company's own projection called for results ranging from a decline of 1% to an increase of 2%.

For September, Macy's expects same-store sales to be down 1% to 3%.

Late Wednesday, fellow department-store owner

J.C. Penney

(JCP) - Get Report

also posted results that beat estimates. The company reported a 4% decline in comps but still topped its guidance for a mid- to high-single-digit decline. Analysts expected a 5.3% drop.

Kohl's

(KSS) - Get Report

was one of few to miss estimates, recording a 0.6% decline in same-store sales, compared with analysts' forecasts for a 2.8% increase.

Luxury retailers performed particularly strongly.

Nordstrom

(JWN) - Get Report

reported a 6.6% jump in same-store sales, topping Wall Street's 6.3% projection.

Saks

(SKS)

recorded an 18.2% surge, nearly doubling analysts' projection for 9.2% growth.

Among the teen chains,

Abercrombie & Fitch

(ANF) - Get Report

reported a 6% increase in August same-store sales, far outpacing predictions for a 2.1% gain by analysts.

At the company's namesake, same-store sales were up 5%. At its children's stores, abercrombie, same-store sales increased 12%. At Hollister, same-store sales increased 6% and at RUEHL, they were up 2%.

American Eagle

(AEO) - Get Report

came out with its same-stores sales results on Wednesday, posting a 9% rise and topping Wall Street's target for a 6% gain.

Todd Slater, an analyst for Lazard Capital Markets, said American Eagle is benefiting from getting its assortments right, helping to drive traffic in the company's mall locations.

"AEO merchants deserve serious kudos for delivering what we see as the most compelling product in the teen space, helping to drive full-priced sales and support margins," he wrote in his research.

Aeropostale

(ARO)

reported a 1.7% rise in same-store sales. That fell below Wall Street estimates for a 2.3% climb.

For

Gap

(GPS) - Get Report

, same-store sales for August decreased 1%, better than analysts' expectations for a 2% slide.

The results were pulled down by weakness at Old Navy, where same-store sales fell 4%. Comps rose 2% at the Gap chain and 7% at Banana Republic. The company indicated, though, that margins were weaker, suggesting the retailer had to mark down items to move merchandise.

"Although merchandise margins were below last year, we're pleased with the progress we're making across our brands," said Sabrina Simmons, executive vice president at Gap.

At

Ann Taylor

(ANN)

, same-store sales rose 2.9%. Analysts had anticipated a fall of 1.9%. At the company's namesake, same-store sales increased 1.7%. For Ann Taylor LOFT, same-store sales declined 1.5%.

Limited Brands

(LTD)

said sales at stores open at least a year rose 1% in August, slightly below analysts' estimates for a 1.4% gain. Same-store sales rose 1% at Bath & Body Works, were flat at the Victoria's Secret chain, and fell 4% at the La Senza chain.

Limited expects same-store sales to be flat in September.