By Katherine Masters

NEW YORK, June 6 (Reuters) - Stocking shelves with low-priced notebooks and slashing prices on sneakers and uniforms, major retailers including Walmart, Foot Locker and Marks & Spencer are preparing for a challenging back-to-school shopping season this year.

U.S. shoppers' spending in the summer ahead of the college and K-12 school year has grown steadily since 2015, according to the National Retail Federation, a trade group. NRF hasn't yet issued an estimate for 2023.

Although shoppers have been spending on essentials this year, they’re much choosier on where to splurge as inflation remains stubbornly high, executives from Ulta, Macy's, Ralph Lauren and Nordstrom said during earnings results over the last two weeks.

On Friday, Doug McMillon, CEO of Walmart, the world's biggest retailer by sales, said at its annual meeting that it would roll out more back-to-school merchandise - notebooks, pencils, pens - at "opening price points" this year. Walmart CFO John David Rainey told investors last week that the retailer, while not immune to "economic whims," is better positioned than others thanks to its reputation for low prices.

Clothing and sneakers previously made up the biggest chunk of back-to-school-related expenses for many families, and Foot Locker said on May 19 that it would rely on promotional discounts to drive demand for sneakers. The chain is stocking Adidas' Samba and Gazelle sneakers ahead of the new school year, it said.

In Britain, where consumers are facing the biggest two-year squeeze in living standards since comparable records started in the 1950s, Marks & Spencer is holding the prices on its school uniform range for a third straight year. Prices start at 7 pounds ($8.69) for a multipack of three cotton unisex polo shirts. M&S is also offering an additional 20% off school uniforms for early shoppers.

The challenge for retailers is predicting whether parents will buy less clothing and sneakers when the cost of necessities - such as pencils, notebooks and laptops - strains many households. Purchases of discretionary goods such as clothing and shoes have fallen since January, according to U.S. Commerce Department data.

Retailers face a "volatile time," said Jessica Ramirez, a senior research analyst at Jane Hali & Associates.

Ratings agency Moody’s in late May predicted “nascent and uneven" operating profit growth overall for global retail and apparel companies this year, with a 6.2% jump in North America-based operating profit following last year's 13% decline.