This study investigated the etiology of longitudinal relations among kindergarten prereading skills, first‐grade word level reading skills, and seventh‐grade reading comprehension in 265 monozygotic and 459 dizygotic twin pairs (Mage = 6.29 years in kindergarten) from the Florida Twin Project on Reading. Using a quadvariate Cholesky decomposition, results showed genetic, shared, and nonshared environmental overlap among prereading skills, word level reading skills, and reading comprehension. In addition, genetic and shared environmental overlap was indicated among word level reading skills and reading comprehension, outside the influence of prereading skills. After accounting for overlapping, there remained moderate genetic and nonshared environmental influence specific to reading comprehension. Implications for reading education are discussed.