Effective Oct. 1, 2013, the official stance on the Boy Scouts of America’s uniform policy is that shirts are to be worn tucked in, regardless of whether the wearer is a Cub Scout, Boy Scout, Varsity Scout, Venturer, or adult Scouter. All Sea Scout uniforms are designed to be tucked in except youth dress whites and youth dress blues.
In the past, guidelines have simply stated the uniform wearer should be neat in appearance. Neatness includes tucking in the shirt. This clarification will appear in related resources, such as the uniform inspection sheets, as they are revised and printed.
This is as published on Scout-Wire, the newsletter for Professionals in the Boy Scouts of America: http://scout-wire.org/2013/10/18/clarification-of-uniform-policy-requires-uniform-shirts-to-be-tucked-in/