Previous research has shown that speech and the interaction of one’s thoughts with others encourage knowledge integration in cooperative problem-solving. However, speech is not always effective and may prevent knowledge integration. This study identified speech types that prevent knowledge integration using a mathematical figure task in cooperative situations. Study 1 generated a hypothesis and tested it through two experiments to identify the speech types that associate with knowledge integration failures in cooperative situations. The results indicated that negative speech toward problem-solving, which hindered the thought process, was associated with knowledge integration failures in cooperative situations. Study 2 examined factors leading to negative speech and found that beliefs such as “math is hard” and “pair partner’s negative speech” promoted their own negative speech. Study 3 examined whether the effects of negative speech affect the speaker or listener. Further, it showed that listening to negative speech hindered knowledge integration. This result suggests that negative speech lowers the efficiency of cooperative group learning. Study 4 clarified the causal relationship between negative speech and knowledge integration using an intervention to suppress negative speech. The results showed that the intervention worked effectively. Moreover, it revealed that a decrease in negative speeches results in better retrieval of knowledge integration performance. Therefore, this study showed that speech might hinder knowledge integration depending on the speech during cooperative learning.
