As an A-List preferred member who always gets pre-assigned seating A-16 or A-17 and who has qualified for multiple years, I was recently traveling with my daughter who is a minor and was assigned B-57. When we approached boarding in the A-List I was stopped by the gate agent and told we needed to board with family boarding. I have travelled SW for atleast 15 years and this never happened.
I believe the gate agent was misinformed as I read that when two people are travelling together (especially a minor) you can board with the lower ticketed passenger. Also, I would assume SW would want to take care of their preferred travelers and allow them to board rather than having to wait until ALL A-List members had boarded.
On Southwest, A-List benefits are granted only to the person who earns them, not any traveling companions. And in the case of an A-Lister traveling with a minor who cannot board by themselves, the A-Lister actually must give up their boarding benefit and board with the minor in either the minor's assigned position or during Family Boarding (if the child qualifies by being age 6 or under), whichever is first.
As your prior experience suggests, many OPS agents do not enforce this rule. But regardless, the official Southwest policy is that any group wanting to board together -- including A-Listers -- should board together at the later position.
Can groups assigned to different boarding positions board together?
Yes. However, in order to maintain the integrity of the boarding process, we ask that earlier boarding positions board with the later positions. For example, if a passenger is assigned position A16 and wants to board with a passenger assigned position A45, the passenger holding the A16 boarding pass should board with the A45 passenger.