Purpose: Reading requires the ability to decode and comprehend. Impairments in working memory (WM) are often implicated in students who are poor decoders. It is unclear whether this is a domain-specific issue or a task-specific issue. Therefore, this study examined how auditory-verbal (AV) WM, visual-spatial (VS) WM, and cognitive load affected the decoding skills of students identified as poor readers. Method: Twenty-five 2nd-grade and 23 fifth-grade students completed 3 different measures requiring various levels of cognitive demand for each domain of WM, and their decoding skills were assessed with word identification and word attack measures. Results: AV WM measures with moderate and high cognitive demands were correlated with 2nd-grade students' abilities to decode words. AV WM measures also predicted their performance on decoding tasks. For 5th-grade students, the AV WM measure with simple cognitive load was correlated with ability to decode words. The VS WM measures were not correlated with word identification or word attack at either level. Conclusions: This study has implications for training instruction in reading. Because the AV WM measures and not the VS WM measures predicted decoding performance in second graders, a greater emphasis on language-rich reading programs could be beneficial in scaffolding early academic achievement and reading performance.