Touchscreens are pervasive in mainstream technologies; they offer novel user interfaces and exciting gestural interactions. However, to interpret and distinguish between the vast ranges of gestural inputs, the devices require users to consistently perform interactions inline with the predefined location, movement and timing parameters of the gesture recognizers. For people with variable motor abilities, particularly hand tremors, performing these input gestures can be extremely challenging and impose limitations on the possible interactions the user can make with the device. In this paper, we examine touchscreen performance and interaction behaviors of motor-impaired users on mobile devices. The primary goal of this work is to measure and understand the variance of touchscreen interaction performances by people with motor-impairments. We conducted a four-week in-the-wild user study with nine participants using a mobile touchscreen device. A Sudoku stimulus application measured their interaction performance abilities during this time. Our results show that not only does interaction performance vary significantly between users, but also that an individual's interaction abilities are significantly different between device sessions. Finally, we propose and evaluate the effect of novel tap gesture recognizers to accommodate for individual variances in touchscreen interactions.