This study investigates inquiry-based interaction and learning outcomes mediated by two types of artifact-centered discourse environments. The study aims to promote social construction of knowledge by optimizing the division of mental effort between pragmatic and semantic grounding activities. We present a theoretical research model by combining social constructivism, grounding theory, and cognitive load theory. We carried out a quasi-experimental study using survey instruments, content analysis, sequential analysis, and knowledge tests for a holistic approach to understand the paradox of mental effort in online learning conversations. The primary finding of this study is that a linked artifact-centered discourse environment facilitates pragmatic grounding activities to attain a common ground in online learning conversations. Additionally, less need for pragmatic grounding activities leaves more room for semantic grounding activities. Finally, more semantic grounding activities lead to a deeper understanding of the learning material.