The current paper explores how students' relationships with their teachers, parents, and friends might differentially impact their academic experience and success, by presenting and integrating the results of two related studies. In the first study, survey methods and structural equation modeling are used to describe the similar and different effects that developmental relationships with teachers, parents, and friends seem to have on middle- and high-school students' academic motivation, GPA, and perceptions of school climate. Relationships with teachers directly predicted all three outcomes at the middle school level, and motivation and school climate at the high school level. Relationships indirectly predicted high school GPA, through motivation. Student-teacher relationships, and parent-teacher relationships, also indirectly predicted middle school GPA, through motivation. Relationships with parents directly predicted only motivation in middle school. Relationships with friends directly predicted school climate at both levels. The results from Study 1 showed the central importance of teacher-student relationships on student motivation and led the research team to qualitatively look in study #2 at how teachers build relationships that motivate students and how students experience those relationships. Study 2 used student focus groups and a grounded theory, open coding approach to analysis to identify commonly occurring themes describing what practices teachers used successfully, in students' eyes, to build strong relationships with students and boost their academic motivation. These practices focused on how teachers expressed care, provided support, challenged students to grow, shared power with them, and expanded their sense of possibilities. The mixed methods produce an overall study that uniquely captures both a global and more granular, practice-oriented view of the ways in which differing developmental relationships in young people's lives affect their connection to and success in school. [This paper will be published in "Contemporary Educational Psychology."]