One of the requirements for Communications Merit Badge is to teach a skill to younger Scouts. THey must first clear it with their merit badge counselor, which is always part of the merit badge process (1st step is to meet with Scoutmaster for approval and sign off on the blue card. 2nd step is to meet with the counselor to understand the rquirements and what he or she expects the Scout to do or demonstrate.)

Also, First Aid has a requirement to teach a First Aid skill to another Scout. That's oriented towards one of the skills required for Tenderfoot, Second Class or First Class rank advanacement.