It is established that male students outperform female students on almost all commonly used physics concept inventories. However, there is significant variation in the factors that contribute to the gap, as well as the direction in which they influence it. It is presently unknown if such a gender gap exists on the relatively new Concise Data Processing Assessment (CDPA) and, therefore, whether gendered actions in the teaching lab might influence--or be influenced by--the gender gap. To begin to get an estimates of the gap, its predictors, and its correlates, we have measured performance on the CDPA at the pretest and post-test level. We have also made observations of how students in mixed-gender partnerships divide their time in the lab. We find a gender gap on the CDPA that persists from pre- to post-test and that is as big as, if not bigger than, similar reported gaps. We also observe compelling differences in how students divide their time in the lab. In mixed-gender pairs, male students tend to monopolize the computer, female and male students tend to share the equipment equally, and female students tend to spend more time on other activities that are not the equipment or computer, such as writing or speaking to peers. We also find no correlation between computer use, when students are presumably working with their data, and performance on the CDPA post-test. In parallel to our analysis, we scrutinize some of the more commonly used approaches to similar data. We argue in favor of more explicitly checking the assumptions associated with the statistical methods that are used and improved reporting and contextualization of effect sizes. Ultimately, we claim no evidence that female students are less capable of learning than their male peers, and we suggest caution when using gain measures to draw conclusions about differences in science classroom performance across gender. [This paper is part of the Focused Collection on Gender in Physics.]