The Black student population underperforms all other demographic groups in high school science achievement. The purpose of this quantitative correlational research was to examine various factors influencing the science proficiency of Black students in selected Florida high schools. Florida's PK--20 Education Information Portal provided the existing data for the school districts sampled (D1 and D2) for this study. Vroom's (1964, 1995) expectancy theory was the theoretical framework used to understand the association between students' science achievement on the Biology I End of Course Exam and their demographics. The research used Pearson's chi-square (X[superscript 2]) and Phi ([phi]) statistics to analyze the relationship between proficiency status and each of three dichotomously coded student demographic variables: (a) gender, (b) economic status, and (c) grade group. The results showed no significant relationship between proficiency status and (a) gender (D1: X[superscript 2] (1) = 0.023, p = 0.880, [phi]= 0.013, D2:X[superscript 2] (1) = 3.908, p= 0.048, [phi]= 0.132) and a moderately significant relationship between (b) economic status (D1: X[superscript 2] (1) = 4.885, p = 0.027, [phi]= 0.187, D2: X[superscript 2] (1) = 8.959, p = 0.003, [phi] = 0.200). The results showed the strongest statistical relationship between proficiency status and (c) grade group (D1: X[superscript 2] (1) = 16.796, p< 0.001, [phi] = -0.346, D2: X[superscript 2] (1) = 34.984, p < 0.001, [phi]= -0.395). The results of this study can inform teachers and policymakers on best practices for narrowing the science achievement gap between Black students and students from other demographic groups. [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.]