This year, shoppers on Long Island and across the nation are expected to do 46 percent of their back-to-school shopping online, up more than 10 percent from last year. And social media will have an increasing influence on what they buy.

Total spending for school and college is expected to increase to $75.8 billion, an 11.5 percent increase from $68 billion last year, according to a National Retail Federation survey. Of that, about $27.3 billion will be spent online.

The average U.S. family with children in grades K-12 plans to spend $673.57 on apparel and accessories, electronics, shoes and school supplies, up from $630.36 last year, said the NRF, a trade association based in Washington, D.C.

Families with college students will spend an average $888.71, down slightly from $899.18 last year, the NRF found. Although average spending will be down for back-to-college, the total spending is expected to be up at $48.5 billion compared with $43.1 billion last year, due to an increase in the number of consumers shopping, NRF said.

Other sales projections are not as robust. The season will see year-over-year growth of 4.2 percent, compared with 3.8 percent in 2015, according to IHS Global Insight economist Chris Christopher.

This year’s expected spending increase comes after a relatively slow year last year, as families focused on buying just the necessities, analysts said. Back-to-school spending is cyclical, often increasing one year as families stock up on supplies, then dropping off the next year as they use longer-lasting items like backpacks or computers for another year. Spending then gets a bump in the third year, when items need to be replaced, NRF found.

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With most Long Island public schools starting classes after Labor Day, the shopping season is just kicking into high gear, said Marshal Cohen, retail analyst with The NPD Group, a Port Washington-based market research company. Shoppers first focus on buying supplies, then clothing and other items as school starts, he said.

While NRF forecast that more than a third of spending will be online this year, IHS predicts a smaller but growing percentage. This year, $1 out of every $5.40 will be spent online, compared with $1 out of $7.50 in 2011, Christopher said.

“When you do your business online, it doesn’t mean you are doing more business,” Cohen said about retailers. “It just means you are moving your business online.”

Free shipping and in-store pickup service are key drivers of online sales. About 84 percent of parents say they won’t shop online without free shipping, according to the NRF.

Quicker shipping times, discount offers and favorable return policies also have made it more desirable, “so people are relying on the convenience,” said Danielle Conte, retail consultant and founder of shopping blog YoutailRetail.com in Centerport. “It is the Amazon effect.”

Social media has influenced what people shop for, both online and in-store. Last year, more than one-third of U.S. teachers used Pinterest and 20 percent used Facebook for classroom curriculum and school list inspiration, NPD found.

“When you have visual social media platforms, like Instagram and Pinterest, you see a lot of opportunities for brands to showcase their apparel, accessories and school supplies,” Conte said. “Social media is going to tell you what is the right look, right color, and the right brand before school starts.”

To help shoppers, Walmart is providing local school supply lists in stores and a generic list on its website. Target has an online School List Assist Tool that displays lists for nearly 1 million schools, including many Long Island districts.

Retailers want to give customers “the chance to shop how they want and when they want,” Walmart spokeswoman Molly Blakeman said.

With a school supply list in hand, Mark Crosson, 48, of Freeport, had his 4-year-old daughter Sophia help pick items such as glue and crayons off the shelves at the Walmart in Uniondale.

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“It is easier to look and pick up stuff in the store than online, said Crosson, whose daughter is starting kindergarten. “She gets to look, too, as we are shopping.”

Frank Petriello, manager of Gail’s Stride Rite Shoes in Port Washington, said the store’s children’s business has grown while the adult side has shrunk.

“Children need to be fitted,” he said. “Adults don’t need to be fitted like before, before the world of the internet.”

He added, back-to-school “is our holiday time of the year.”