This study investigated how demographics predict mathematics achievement development and how such development predicts academic ability and job income expectations. A hypothesis model was examined through growth modeling with data collected from students studying in grades 7, 9, 11, and 12 in Taiwan (n = 4163). Data analysis revealed that the hypothesis model exhibited a good fit to the data. Compared with girls, boys exhibited higher mathematics achievement in both the start and growth of mathematics achievement. Parental education and speaking Mandarin and Taiwanese Hokkien at home played roles in both the start and growth of mathematics achievement. Speaking English at home exerted a positive effect on the start but not the growth of mathematics achievement. Speaking other foreign languages and Formosan languages at home exerted negative effects on both the start and growth of mathematics achievement. Family income and urban residence exerted a positive effect on the start but not the growth of mathematics achievement. Remote residence exerted a negative effect on the start but a positive effect on the growth of mathematics achievement. Both the start and growth of mathematics achievement played a role in students’ expectations of academic ability and job income.