This study investigated different subtypes of poor readers, following an original group of 213 children from kindergarten to Grade 2. Four groups were formed on the basis of their performance on three reading comprehension tests varying in their processing demands: a WJPC-Low group (Woodcock-Johnson Passage Comprehension test; n = 27), a CBM-Maze-Low group (Curriculum-based Measurement-Maze Test; n = 18), a Recall-Low group (n = 19), and a control group exhibiting no deficits (n=30). All groups of poor readers performed at least one standard deviation below the average age group mean on the respective test used for their identification. The four groups were identified in Grade 2, and they were compared retrospectively in Grade 1 and Kindergarten on a set of cognitive and linguistic measures. The effects of verbal and nonverbal ability, age, and parental education were controlled among the groups. Results showed that the CBM-Maze-Low group exhibited relatively low performance on most linguistic component skills such as RAN, phonological ability, word reading fluency and accuracy, across all three time points. The WJPC-Low and the Recall-Low groups, in contrast, consisted of readers who performed relatively low on word reading fluency and phonological measures only, in Grade 1 and 2 but not in Kindergarten. There were no differences in any of the cognitive measures. Implications of the findings for the use of reading comprehension tests as diagnostic tools are discussed.