Research Findings: Universal screening is the first stage in identifying students at risk for reading difficulties within a Response to Intervention model. However, there is a lack of validated screening tools for assessing reading abilities in first-grade students from Spain. This pilot study examines the technical adequacy, classification accuracy, and best predictors within a set of curriculum-based measures (CBMs) in Spanish. A sample of 178 first graders from urban and peripheral areas of Santa Cruz de Tenerife (the Canary Islands, Spain) was assessed in the fall, winter, and spring. Receiver operating characteristic curves and logistic regression models were conducted to evaluate the predictive validity of each CBM and their composite score. In addition, students' learning growth on each CBM was analyzed using hierarchical linear models. Although results suggested that most of the CBMs had adequate reliability and validity throughout first grade and were able to detect students' growth, some measures showed low reliability and validity coefficients. Practice or Policy: Some of the studied CBMs could potentially be used as universal screening to early detect reading difficulties in this population. A two-stage gated screening procedure is proposed for future research and practical implementation using oral reading fluency in the first step.