NEW YORK — As the back-to-school selling season winds down, retailers across the country are pointing to basic stonewash jeans as the leader of the pack.

Back-to-school, which starts in July and hits full stride in August, is denim’s most important time of year, as vital to that category as Christmas is to fruitcake. While not all stores were willing to share specific results, two of the nation’s biggest chains — J.C. Penney Co. and Sears, Roebuck & Co. — each cited double-digit gains, and two other retailers — Macy’s East and Venture Stores — each called their jeans business “healthy.”

From mass merchants to department stores, the five-pocket style has been the volume seller. Some dark colors such as deep indigo and black showed life, while shades such as green and wine, which were key last year, haven’t been as strong this time.

Surface treatments that make jeans look used — sandblasting and stonewashing, for example — or actual vintage jeans, continue to be the preferred looks.

A few fashion trends have crossed over from junior fashion. Suspender shorts and jeans, short skirts in various silhouettes and overalls showed gains this fall. One mass store reported that tight Lycra spandex and cotton jeans emerged as a strong back-to-school seller. Items such as jackets and vests got tighter and more cropped.

Here, a cross-section of stores reports on top trends.

Back-to-school denim business at J.C. Penney finished 20 percent ahead in August, when the chain sold at least one million pairs of jeans, according to Bob Schmid, a jeans buyer.

“Business kicked in with a vengeance about the middle of August,” said Schmid. “And the shift is away from colored jeans. Basic denim looks in basic washes are about 70 percent of the business.”

Classic fit jeans are generating 60 percent of sales, with relaxed fit making up most of the rest.

Arizona Jeans Co., which is Penney’s private label, along with Levi’s, were the top dollar vendors. Arizona classic fit styles, reduced $2 to $17.99, and Levi’s 550 jeans, reduced $5 to $29.99, were bestsellers.

During August, Penney’s sold about 400,000 pairs of Levi jeans, 75 percent of which were 550s, and about 600,000 pairs of various Arizona jeans.

At Sears, a spokeswoman said shorts business was up in double digits over last year, and that long jeans business started at the end of July, an earlier shift than last year.

Outside of basic indigo washes, natural has been the top color, and the best-selling overall was a relaxed five-pocket style.

“Lee is up substantially over last year, and Levi is still very strong,” the Sears spokeswoman noted. “We are also seeing the emergence of suspender jeans and suspender shorts.”

At Macy’s East, a spokeswoman said denim sales in the junior area have been “healthy” and ahead of last year, but she declined to say by how much. The store recently brought in vintage Levi’s, which have been selling far above expectations.

“Levi’s 550s and 512s have been nonstop,” she noted. Levi’s ran a month-long, storewide promotion at Macy’s East stores in August.

Stonewashed jeans have been a popular surface treatment, the spokeswoman said, and overdyed dark indigo jeans from Guess and Bongo have emerged as a new trend. Top items during the month included a bleached and fitted vest from Breaker, as well as short denim scooter and A-line skirts and kilts in dark colors.

A Kmart spokesman said that there, too, the business has been basics. However, Lycra spandex and cotton tight jeans in overdyed indigo were a key item for August sales.

Gregory Blow, director of fashion merchandise at Venture Stores, said that while the basic five-pocket is “the fundamental and the base” for the junior customer, there are new dimensions to the category such as sleeveless fitted denim shirts, long and short dresses, and denim kilts, minis and long slim styles.

“The best color is the softly washed blue,” said Blow, who characterized gains in denim as “healthy.”

At Knoxville, Tenn.-based Goody’s, back-to-school business consisted primarily of basic five-pocket styles in stonewashed, bleached and natural finishes. Relaxed fit performed best in misses’ sizes, while juniors preferred a tighter, classic silhouette, according to Kris Rice, denim buyer.

Whereas Goody’s promoted colored denim heavily at entry prices last year, the chain relied on natural and hunter shades this season. Shorts, which have been strong all summer, continued as good items for fall, as did suspender denim shorts and pants.