For your Sim to be promoted, he or she must have enough skills and a requisite number of friends.

Check the "job" button to see the status of your Sim's job.

Also check that the Sim has a positive mood rating as shown by the bars above and below the "mood" icon. These will change as individual needs are met or neglected. If the mood bar is neutral or negative when the carpool arrives, the Sim will probably not be promoted.

Remember that the last thing to affect a Sim's mood is the walk to the carpool, which may change their "room" need. A depressing yard can dampen his or her spirits immediately before leaving for work.