When sociologists examine how far an individual moves up or down the socioeconomic scale in his or her lifetime, they are studying: ?

I believe the answer is: intragenerational mobility

The measurements that used for intragenerational mobility would is most commonly through economic wealth comparison between the subject and the subject's parents. If the average income of the subject is significantly higher compared to his/her parents, we can conclude that the subject has move up in the intragenerational mobility