Motivation impacts student academic performance. A performance task to directly assess writing motivation in young children is needed. The purpose of this investigation was to evaluate the validity of the Writing Challenge Task (WCT), a task-oriented assessment created to measure writing motivation with 106 kindergarten students in the rural mid-South. The authors sought to establish internal reliability; concurrent validity with the Motivation for Reading and Writing Profile (MWRP); evaluate correlations between measures and socioeconomic status (SES); and evaluate the predictive validity of the WCT to a state-mandated end-of-year assessment. Cronbach's alpha, a correlation analysis, and stepwise multiple regression analysis were used to examine these relationships. The WCT had excellent internal reliability with Cronbach's alpha of 0.91 (n = 64). The WCT (p = 0.01) and SES (p = 0.03) were both positively correlated with end-of-year writing scores, though the MRWP was not. No significant correlations between the WCT, the MRWP, and SES were found. Further, the inclusion of WCT as a predictor created the most robust model so that predictor variance (SES and WCT) accounted for 11% of the variance in end-of-year writing scores, p = 0.01, R[superscript 2] = 0.11, such that students were expected to score 0.13 units higher on the end-of-year writing assessment for every 1 point increase in their WCT score. This study established evidence that students' WCT scores had higher predictive validity on kindergarteners' end-of-year outcomes than a more commonly used writing motivation instrument. Future research on the measure is warranted.