This dissertation focused on the outcome of elementary science teachers' learning in theories and practices of epistemic tools in professional workshops over the course of two years, starting in the summer of 2019. Study one focuses on teachers' understanding of language as an epistemic tool. The data were teachers' written responses to a vignette. In their responses, teachers gave advice to Naomi, the science teacher in the vignette, about how to use language in the science classroom and explain the importance of the use of language. The teachers' written data were collected in the summer of 2020, one year after teachers first learned the concepts of epistemic tools. Purposeful sampling was used to select teachers' written responses to find similarities and differences in teachers' understanding. All teachers were ranked based on the total scores of a questionnaire measuring teachers' knowledge of the language as an epistemic tool (Fulmer et al., 2021). Fifteen teachers on the top were selected as Group 1, and another fifteen teachers from bottom were selected as Group 2. With Gee's theory of critical discourse analysis (CDA), it was found that both groups of teachers had similar understanding about how to use language to teach, that is, the pedagogical understanding. However, the two groups of teachers had different understanding of the relationship between language and learning, that is, epistemic understanding: Group 1 teachers emphasized the relationship between writing and learning more than Group 2 teachers' understanding. Study two focuses on the shift of teachers' epistemic orientation over time. A short version of the epistemic orientation survey (S-EOS) adapted from Suh et al. (2021) was used for data collection. The S-EOS, which has 35 items with four subdomains on a five-point Likert scale, was repeatedly distributed on four occasions. The interval between adjacent occasions was approximately six months. The four subdomains include knowledge construction (KC), knowledge replication (KR), classroom authority (CA), and epistemic nature of knowledge (ENK). By employing the curve-of-factors model (CFM), the first-order factors had a partial residual variance invariance model, based on which the growth curve for the second-order factors tracked the change of teachers' epistemic orientation over time. It was found that teachers' epistemic orientation grew fast in the first six months of the workshops and reached the peak of the magnitude. After six months, the magnitude of epistemic orientation continually declined at a much slower rate compared to the growth rate in the first six months. In addition, when each of the subdomain's growth curves was examined, it was found that only KC had a continuous growth pattern over time, and the growth rate was faster in the first six months compared to the growth rates after the six months. Thus, KC is the primary contributor to epistemic orientation growth. In conclusion, the vignette analysis showed that teachers had a similar pedagogical understanding of using language in science classrooms regardless of the language questionnaire scores. However, teachers with higher questionnaire scores emphasized the relationship between writing and learning, which underlies the epistemic understanding of language. The analysis of teachers' epistemic orientation change with growth modeling showed fast growth in the first six months, and teachers' epistemic orientation appeared to stay the same after that. Also, knowledge construction was a main contributor to the growth of epistemic orientation. Combining results from two studies found that teachers' learning of epistemic tools positively influenced their epistemic orientation. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]