As of 4th grade, youth are ready to take on a bit more intensive and independent outdoor and service oriented adventures. Their requirements build on what's been learned already and look ahead to the kind of youth-led activities they'll do when they bridge to a Scouts BSA Troop in spring of 5th grade. (Troops are kind of like the secondary school version of Cub Scouts.)
Read more about the Advancement Trail for Cub scouts, including what's expected at each rank level from Lion (Kindergarten) through Webelos and Arrow of Light (5th grade), here.