Fluency is a key element in the development of foreign language and assesses the learner\\\'s proficiency and competence in speech. One way to examine this is through utterance and cognitive fluency, aspects personal to the speaker. Utterance fluency pertains to the timing, pauses, and correction features of spoken utterances, whereas cognitive fluency relates to the speaker’s ability to engage the fundamental cognitive processes needed for smooth speech production. The main goal of the current mixed method study is to investigate the relationship between cognitive and utterance fluency and how grammatical knowledge and proficiency affect a particular area of linguistic knowledge. Drawing on Albino’s (2017) framework, a quasi-experimental design was employed using video clips and semi-structured interviews. The study recruited 42 Iranian learners of English who were at the higher-intermediate level of language learning. The intervention took place over eight weeks, with the students attending 2 x 40-minute sessions per week. After approving the normal distribution of the collected data, t-test and Pearson correlation were used to analyze the data. The analysis identified several statistically significant relationships between fluency processing, syntactical knowledge, and cognitive processing. The analysis also revealed that cognitive processing impacted utterance fluency, and processing skills impacted syntactical structure knowledge. The research supports Kahng\\\'s (2014, 2020) perspectives, demonstrating that grammatical knowledge and proficiency significantly impact linguistic knowledge. Further, the results suggest value in providing learners with exposure to real-world scenarios, which was viewed as effective in supporting fluency.

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