This study explored how teachers engage and support students at a project-based STEM high school to identify key elements defining students' learning experiences in a project-based environment. Interviews and surveys provided students' and teachers' perspectives of challenges and supports in the project-based learning process. The teachers' support was personal and caring, they challenged students and provided responsive guidance and advice, responding directly to students' interests while retaining high standards and expectations; we saw that teachers' caring in an environment of high expectations was crucial for student success. Identification of three critical elements of the teachers' supports and challenges (student-centered projects, a focus on twenty-first century competencies, and strong teacher-student relationships) led to recommendations for teacher preparation such as providing preservice teachers with authentic experiences, celebrating failure as part of learning, explicitly teaching about project-based learning pedagogy, and stressing the importance of caring relationships and twenty-first century competencies.