In its latest forecast on back-to-school shopping, eMarketer expects ecommerce to encompass nearly 10% of all US back-to-school sales this year.

Overall back-to-school season sales are projected to rise 3.5% this year, reaching $885.2 billion. The 3.5% increase is slightly less than the 3.7% gain registered in 2017.

Meanwhile, ecommerce sales are expected to rise 15.4% during the months of July and August, totaling $85.55 billion. This year’s increase tops the 15% gain logged in 2017.

eMarketer also breaks out ecommerce spending into “core” seasonal purchases, which include apparel and accessories, books/music/video, computers and consumer electronics, office equipment and supplies, and toys/hobby. For these categories, total online spending is expected to rise 14.3%.

In contrast to eMarketer’s forecast, the National Retail Federation projects that back-to-school sales will edge down slightly this year. While back-to-college spending will rise a bit, the NRF said, spending associated with school-age children will decline.

Not everyone agrees, however, on when the back-to-school season starts. While eMarketer’s data is comprised of back-to-school sales in July and August, the growing clout of Amazon has led many retailers to peg the start of the season to Prime Day. A study by Cardlytics found that despite 73% of back-to-school shoppers buying school supplies only in-store last year, Prime Day had the effect of shifting shoppers' spend up by nearly one month.