This longitudinal study analyzes survey responses in seventh, eighth, and ninth grade from diverse public school students (n = 482) to explore gender differences in engineering and science career preferences. Females were far more likely to express interest in a science career (31%) than an engineering career (13%), while the reverse was true for males (58% in engineering, 39% in science). After controlling for student and school demographic characteristics, females were as consistent as males in their science career interests during the three years of the study but less consistent in their engineering career interests. Knowing an engineer significantly predicted consistent career interest in engineering for males but not for females. Childhood interest in science and engineering was related to whether females and males expressed any interest in those subjects. Females and males both showed interest for careers where they can discover new things that help the environment or people's health; females were less interested in designing and inventing, solving problems, and using technology. These findings suggest that increasing the number of diverse students who pursue engineering careers may require introducing students from early elementary to middle school to engineering as an array of careers that can improve health, happiness, and safety, and make the world a better place.