Science scores among US fourth-grade students have declined compared to their international counterparts in recent years. Recent results show that teachers are the most impactful influence on student success and accountability. Teacher preparedness and professional development are two key areas that serve as indicators of providing relevant and essential information for students' success. A correlational quantitative study was conducted to assess the relationship between teacher preparedness and professional development on fourth-grade students' science achievement. The TIMSS 2019 data were secured from the Boston College, TIMSS, and PIRLS International websites. The data was evaluated using the SPSS 27 Hierarchical Linear Regression. The study's population included 70 teachers and 1208 students representing schools located in the United States. Results indicated that teachers who graduate with science majors have the greatest impact on students' science outcomes. Specific professional development topics that teachers studied also served as key indicators of student science success. Topics that specify the objectives found in the "Next Generation Science" curriculum had the greatest impact. The topics included future science pedagogy, critical thinking, and past and future student needs. Thus, recruitment of teachers with science majors should be the focus of human resources recruitment officers, and quality, well-developed professional development must focus on the "Next Generation Science Curriculum."