In my troop, we have a problem with certain new scout parents approaching the SPL and ASPL for signing off on their kids' advancements. I am an ASPL in the troop, and I am bothered by what i see is parental interference along a trail that should be driven by a boy himself. I have attempted to refuse on many occasions, but I get the constant wheedling of "just do it", or a "you're just being difficult". I feel the need to put my foot down, and politely tell the offending adults to back off. Do you suggest that as a good course of action?

Stand your ground and politely suggest the parents speak with the Scoutmaster. Parents should not be dealing with the Scouts but with Scoutmaster and Assistant Scoutmaster.

To expand on my answer. I think you should discuss this with your Scoutmaster so he is aware of what is happening and is not blind sided by some parent.

As far as handling the parent you can say something like "I would be happy to review what is required to fulfill this requirement with your son Jimmy Mrs. Jones. However, if you like, please feel free to discuss this with the Scoutmaster."

The parent will either let it drop or will be in for an awakening when the Scoutmaster explains how things work in a Troop and how it is different from Cub Scouts.

Hope this helps!

It is true that the parents should be guided to the SM / ASM
Another point is that while the parent can ask, you could also remind them that if their son has done the requirement, then there should not be an issue for you to test their son, after all, that by signing the book, you are verifying that the scout can perform the skill confidently.

One of the goals of scouting is to have fun and learn at the same time...doing things once does not qualify as having learned the skill. Hope this helps