Motivation is a key factor in engagement, achievement, and career choices in science, technology, engineering, and mathematics (STEM). While existing research has focused on student motivation toward math in formal school programs, new work is needed that focuses on motivation for those involved in informal STEM programs. Specifically, the role of math mindset and perceived inclusivity of informal STEM sites (to those of varying gender and ethnic backgrounds) on longitudinal trajectories of adolescents’ math motivation has not been explored. This study investigates longitudinal changes in math expectancy, interest, and utility values and the effects of math fixed mindset, math growth mindset, and perceptions of the inclusivity of informal STEM learning sites on these changes for adolescents participating in STEM programs at these informal sites in the United Kingdom and the United States (n = 249, M_T1age = 15.2, SD = 1.59). Three latent growth curve models were tested. The data suggest that math expectancy, interest, and utility values declined over three years. Growth mindset positively predicted changes in utility, while fixed mindset negatively predicted changes in utility. Inclusivity positively influenced the initial levels of utility. Girls reported lower initial expectancy than boys. Age influenced both the initial levels and rate of change for expectancy. Older adolescents had lower levels of expectancy compared to their younger counterparts; however, they had a less steep decline in expectancy over three years. These findings suggest that designing inclusive learning environments and promoting growth mindset may encourage math motivation.

动机是科学、技术、工程和数学 (STEM) 领域参与度、成就和职业选择的关键因素。虽然现有的研究重点关注学生在正规学校课程中学习数学的动机，但需要新的研究来关注那些参与非正式 STEM 课程的学生的动机。具体而言，尚未探讨数学思维方式和非正式 STEM 网站（对不同性别和种族背景的网站）的包容性对青少年数学动机纵向轨迹的影响。本研究调查了数学预期、兴趣和效用值的纵向变化，以及数学固定心态、数学成长心态和对非正式 STEM 学习网站包容性的看法对参与这些非正式网站的 STEM 项目的青少年的影响。英国和美国（n  = 249，M _T1age  = 15.2，SD  = 1.59）。测试了三种潜在生长曲线模型。数据表明，三年来，数学期望、兴趣和效用价值均有所下降。成长心态积极预测效用的变化，而固定心态消极预测效用的变化。包容性对最初的效用水平产生了积极影响。女孩的初始预期低于男孩。年龄影响预期的初始水平和变化率。与年轻青少年相比，年龄较大的青少年的预期水平较低；然而，三年来他们的预期下降幅度较小。这些发现表明，设计包容性学习环境和促进成长心态可能会鼓励数学动机。