Thanks to significant product discounts and promised rebates, the Lincolnshire school could save up to $250,000 on athletic gear over the life of the sponsorship agreement, Stevenson spokesman Jim Conrey said.
"What makes this agreement a victory is the fact that we're going to save money without compromising the quality of our athletic program," he said.
The deal is with a Dallas apparel and equipment distributor called BSN Sports rather than Under Armour directly. Baltimore-based Under Armour doesn't sell its products directly to schools, Conrey said.
BSN already provides most of Stevenson's athletic gear, school officials said.
Under Armour approached Stevenson officials about an exclusive agreement for uniforms and equipment in June. Stevenson officials then sought competitive bids from apparel suppliers, asking for brand-specific proposals.
Pricing and customer service were among the factors Stevenson officials considered, Conrey said. The Stevenson High board settled on BSN and approved the contract Monday night.
It's effective immediately.
Representatives of Under Armour or BSN couldn't be reached for comment.
During the 2016-17 school year, Stevenson had 814 varsity athletes on 39 teams. They -- and the school's other student athletes -- wore gear from Under Armour, Nike, Adidas and other companies.
Teams that need to switch brands can do so when they next buy uniforms as part of their regular replacement cycle, Athletic Director Trish Betthauser said.
If Under Armour doesn't make a desired piece of equipment, Stevenson is free to use a different manufacturer. For example, Stevenson's football players use Riddell helmets, and that will continue.
Teams will continue to make their own preferences for practice attire, Betthauser said, but Under Armour practice gear will be available at a discounted price.
Although the agreement doesn't apply to non-varsity teams, such squads likely will buy Under Armour uniforms when it's time to replace them because of the low pricing, Betthauser said.
As part of the deal, discounted spirit wear, footwear and other accessories made by Under Armour also will be made available to student athletes and their families, Betthauser said.