Although the study of metamemory monitoring originated in predictions for simple span tasks, the study of metacognition for working memory (WM) has been somewhat neglected in comparison with long-term memory. We aimed to fill this gap by exploring the ability to self-assess WM operations. Thirty-four participants performed 16 series of complex span tasks and rated their confidence in a verbal recall paradigm. We manipulated the cognitive load based on the TBRS model in order to analyze the role of attentional resources on both WM and metacognitive evaluations. As expected, we found that recall is affected by cognitive load and we found standard serial position effects. Interestingly, metacognitive evaluations followed the same pattern, and measures of metacognitive sensitivity suggest that participants are able to make item-by-item retrospective judgments reflective of their performance. We discuss how these results contribute to our understanding of metacognitive access to newly-formed WM contents.