This paper describes an in-class activity to introduce random assignment, paired data, and learning effect. The activity requires minimal materials, can be completed in a single class period, and is suitable for those using technology to conduct data exploration but can also be adapted for use in a technology-free classroom. The activity consists of students filling in two lines of circles, one using their dominant and the other using their nondominant hand. The difference in time to fill in the circles is compared. Results typically show a significant difference in time to fill in circles with the nondominant hand taking significantly longer, a significant learning effect, and a difference in time to fill in circles using a pencil compared to pen.