Home language (HL) effects on academic language literacy have been extensively discussed. However, previous research has mostly focused on Indo--European languages. This study extends the literature by using data (n = 17,600) collected in a diversified language area: Guangxi, China. We examined the effects of four HLs and four socioeconomic factors by using modern standard written Chinese literacy as an outcome across three developmental levels (ages 10.45, 12.31, and 14.72). School clustering effect existed and adding the predictors of HL and socioeconomic status did not change the variance proportion in literacy performance accounted for by the school groupings. The findings indicate that (a) Putonghua-only speakers performed poorest in school Grades 5 to 6 and 7 to 8, (b) dominant Putonghua speakers performed best in Grades 7 to 8, (c) heritage-only speakers performed best in Grades 5 to 6, and (d) the contribution of the parents' socioeconomic factors depended on the participants' developmental levels. Our study supports the bilingual literacy advantage and explains why a heritage-only acts as a type of bilingualism.