This study assessed the effects of sampling breadth on technical features of word identification fluency (WIF), a tool for screening and monitoring the reading development of first graders. From a potential pool of 704 first-grade students, the authors measured both a representative sample (n = 284) and 2 other subgroups: those with low reading achievement (n = 202) and those with high/average achievement (n = 213). Data were collected weekly on broadly and narrowly sampled WIF lists for 15 weeks and on criterion measures in the fall and spring. Broad lists were developed by sampling words from 500 high-frequency words, whereas narrow lists were created by sampling from the 133 words from Dolch preprimer, primer, and first-grade word lists. Overall, predictive validity for performance level, predictive validity for growth, and commonality analysis showed narrow sampling was better for screening the representative group and the high/average subgroup. Broad sampling was superior for screening the low-achieving subgroup and for progress monitoring across groups. (Contains 8 tables.)