  We analyze language change over time in a collaborative, goal-oriented
instructional task, where utility-maximizing participants form conventions and
increase their expertise. Prior work studied such scenarios mostly in the
context of reference games, and consistently found that language complexity is
reduced along multiple dimensions, such as utterance length, as conventions are
formed. In contrast, we find that, given the ability to increase instruction
utility, instructors increase language complexity along these previously
studied dimensions to better collaborate with increasingly skilled instruction
followers.
