Seating that allows movement is commonly suggested to enhance postural activation, attention, and behavior. The study examined the effects of ball chair seating on legibility, student behavior, and classroom productivity. In two consecutive years, in an ABAB design, first grade students alternated by weeks between standard seating (A phases) and ball chairs (B phases) during math class. Parents provided informed consent for student to be included in analysis (11/16 Year 1; 19/25 Year 2). There were significant decreases in legibility across the phases of this study (p <0.001). Time in Seat was greater in each of the B phases compared to the first A phase (p <0.001). There were no significant differences in the proportion of instructions followed (p =0.564). There were differences in undesired behaviors: each switch to ball chairs was accompanied by a nonsignificant decrease in undesired behaviors, but the increase in undesired behaviors switching back to standard chairs was significant (p =0.004). There was no difference in the proportion of time spent productively (p =0.723). The effect on legibility suggests that if the desired outcome is improved legibility, using ball chairs may not serve as an effective intervention. The effects on behavior suggest that implementing a classroom-wide alternative seating intervention may have moderate, reversible positive effect. The effect on productivity suggests that ball chairs do not disrupt, nor enhance, classroom efficiency.