University Teaching Experience for Mathematics Prospective Teachers (UTEMPT), an NSF-funded collaborative project, has implemented an innovative version of early field experiences in order to provide preservice mathematics teachers an opportunity to make a meaningful connection between methods-course-content and teaching practices in a college setting. As part of the multisite UTEMPT project, this study reports the impact of a campus-based early field experience for secondary preservice mathematics teachers through data collected at Penn State University. The purpose of this study is to examine the impact of the implementation of a University Teaching Experience (UTE; Bieda et al., 2017) model on secondary mathematics preservice teachers' instructional visions over the semester. Two theoretical frameworks ground this study: the "UTE model" as a conceptual framework and "visions of high-quality mathematics instruction" (VHQMI; Munter, 2014) as an analytical framework. To this end, this study seeks to assess the following: the overall impact of UTE, changes in VHQMI, and student perceptions of the intervening UTE model. To fully explore these elements, this study drew on in-depth interviews, reflection papers, and final papers from a control group in spring 2018 and two experimental cohorts: an in-person cohort in spring 2019 and a semi-online cohort in spring 2020. Thirty preservice teachers participated across the three cohorts in this study. The implementation of a semi-online format of treatment was unplanned and was necessitated in response to the COVID-19 pandemic. The data was explored both quantitatively (Phases 1 and 2: non-parametric statistics) and qualitatively (Phase 3: inductive thematic analysis). The statistical analyses reveal that the most significant overall impact and changes in instructional visions occurred in the in-person cohort. Qualitative analysis of those preservice teachers' statements revealed that the close supervision aspect was most helpful to the participants and the participants advocated for further use of the UTE model; participants in this cohort made a markedly small number of negative comments. The findings indicate that the early field experience afforded the preservice teachers an opportunity to learn about and practice the complexities of mathematics teaching in a supportive environment. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]