The goal of Head Start is to develop the cognitive and social-emotional skills of children from low-income families to prepare them to succeed in kindergarten and beyond. Presently, Houston Independent School District (HISD) collaborates with four federally-funded Head Start agencies: AVANCE, Gulf Coast Community Services Association (GCCSA), Harris County Department of Education (HCDE), and Neighborhood Centers, Inc. (NCI). Each Head Start agency provides, not only high-quality educational programs to 3- or 4-year-old low income children, but also offers access to health, dental, and other support services in order to meet families' needs. The purpose of this report was to explore the lasting impact of Head Start on students' performance on the third grade STAAR reading and mathematics tests. The findings suggested that economically-disadvantaged students who attended Head Start programs obtained higher mean scale scores, and had higher percentages of students who met the 2015 STAAR Level II: Satisfactory (Phase-In 1) standard on both third grade reading and mathematics tests than their peers in the district. Among the four Head Start agencies, NCI had the highest percentage of students who met the 2015 STAAR Level II: Satisfactory (Phase-In 1) standard on the third grade reading and mathematics tests, and obtained the highest mean scale scores on the 2015 STAAR reading and mathematics tests.