Since the 2017-2018 academic year, Montgomery Public Schools (MCPS) has invested in the Two-Way Immersion (TWI) program, across six elementary schools, aiming to cultivate bilingualism, biliteracy, and biculturalism among students from Kindergarten through Grade 5. As part of this initiative, this comprehensive study assessed the implementation and outcomes of the TWI program, building on previous evaluations conducted by MCPS and the Center for Applied Linguistics (CAL). This evaluation utilized a mixed-methods approach, gathering data from teacher surveys (36% response rate), staff surveys (44% response rate), and parent surveys (8% response rate), along with interviews with school principals (n=4) and Dual Language Coaches (DLC) (n=7). Quantitative data were analyzed using descriptive statistics and statistical modeling to assess academic performance and language proficiency, while qualitative data from survey responses and interviews offered valuable insights into stakeholders' experiences and the program's implementation. The MCPS Two-Way Immersion (TWI) program made progress implementing assessments to measure dual-language education, particularly with Spanish math assessments which were implemented across Kindergarten-Grade 5, with more than 80% of teachers and staff rating them as effective. However, the program faced substantial challenges in implementing Spanish literacy assessments during the 2023-2024 academic year. More than 40% of teachers and staff rated these assessments poorly, and there was no external literacy assessment in Spanish for Grades 3-5. Furthermore, 62.7% of teachers and 58.5% of staff reported that measuring literacy progress was 'Not Going Very Well' or 'Not Well at All.' One respondent emphasized the "...lack of consistent tools for monitoring Spanish literacy progress." While English proficiency assessments were adequately provided, the absence of a dedicated assessment to measure Spanish language acquisition remains a critical gap. Over 60% of staff identified this as a significant issue, highlighting the need for more effective tools to evaluate Spanish language skills in TWI students. Despite these challenges, teachers and staff reported positive collaboration and data-driven instructional planning, though further improvements are needed in Spanish literacy assessments and proficiency measures.