There are a few pay grades in the army for which there are a couple of different ranks--E-4 can be a Specialist or a Corporal, E-8 can be a Master Sergeant or a 1st Sergeant, and E-9 can be a Sergeant Major, a Command Sergeant Major, or the Command Sergeant Major of the Army. There must be a good, legitimate reason to move laterally from one rank to another within a pay grade.
Although the orders came in last week dated and April 1st, today my son pinned on the rank and became the army's newest corporal. The difference between a specialist and a corporal is significant--a specialist is a "lower enlisted rank", whereas a corporal is a non-commissioned officer. This lateral move involves no pay raise but does come with the prestige of being an NCO at age 20.
There are a few reasons he was advanced to this rank. First, he's done extremely well in the army, better than even I thought he would. Second, he's a team leader, which means he's the direct supervisor of another soldier. And third, he's already passed the promotion board for sergeant, so all he needs now is to earn enough "promotion points" (which he's working on!) and then he'll be promoted to E-5/sergeant. His current rank is thus CPL (P), for promotable.
I'm very proud of the army's newest NCO.