From the Times:

Helmets both new and used are not -- and have never been -- formally tested against the forces believed to cause concussions. The industry, which receives no governmental or other independent oversight, requires helmets for players of all ages to withstand only the extremely high-level force that would otherwise fracture skulls. 

The standard has not changed meaningfully since it was written in 1973, despite rising concussion rates in youth football and the growing awareness of how the injury can cause significant short- and long-term problems with memory, depression and other cognitive functions, especially in children. Moreover, used helmets worn by the vast majority of young players encountered stark lapses in the industry's few safety procedures. 

Some of the businesses that recondition helmets ignored testing rules, performed the tests incorrectly or returned helmets that were still in poor condition. More than 100,000 children are wearing helmets too old to provide adequate protection—and perhaps half a million more are wearing potentially unsafe helmets that require critical examination, according to interviews with experts and industry data.