Back-to-school season is one of the busiest for massive retailers like Walmart Stores Inc. (WMT) and Amazon.com Inc. (AMZN) as well as specialized players like Staples Inc. (SPLS) . They're all eager to sell classroom supplies to parents and kids alike.

A quarter of U.S. households participate in back-to-school shopping, according to a Deloitte survey, and the season accounts for about half of school-related spending. Some 29 million households, shopping for 53 million children, will spend $27 billion in 2017, Deloitte estimates. Brick-and-mortar chains still reign supreme, with the average consumer spending $288 in-store versus $103 online. More than a third of survey respondents expect to visit online-only retailers, flat year over year.

Staples, set to be acquired by private equity firm Sycamore Partners for $6.9 billion, is highlighting its business-to-business operations as consumers increasingly eschew big brick-and-mortar retailers in favor of online shopping. Back-to-school is still one of Staples' most important shopping seasons, however, and with the company's 110% Price Match Guarantee you're unlikely to find better prices on items like 50 cent notebooks and 64-packs of Crayola crayons for $3. Office supply chains are less popular these days, however, with 33% of respondents in the Deloitte survey expecting to visit them, down 9% from last year.

Amazon, once just a book retailer, is a favorite for college students. It has discounted some of its most popular gadgets accordingly, including Echo home assistants, Kindle e-readers and Fire tablets. Unsurprisingly, it's a solid choice for electronics like the $55.95 scientific calculators, a must for classroom. Beyond gadgets, Amazon is one of many places to find that tried-and-true staple No. 2 pencils.

Since its $3.3 billion acquisition of Amazon rival Jet.com last year, Walmart has ramped up its online capabilities and variety. The JanSport Classic SuperBreak Backpack, available on Walmart.com for $29.95 in navy, may not be the cheapest backpack around, but its sturdiness means it's more than worth the price and will last more than one school year. The backpack and tons of other items, like Westcott plastic rulers, are available with free store pickup and Amazon-style shipping in two days. And mass merchants like Walmart are by far the most popular category for back-to-school shoppers: 81% plan to visit one, up 24%.

Here are some back to school tax holidays.

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