The study investigated the effects of children-generated illustrations and gender on pupils' achievement in phonics in the Udenu Local Government Area of Nigeria. The study employed a non-equivalent quasi-experimental 2 x 2 factorial research design. Some 172 primary two pupils from 4 schools were used for the study. The English Achievement Test (EAT) was used to collect data. Three hypotheses were tested. The data were analysed using descriptive statistics and Analysis of Covariance (ANCOVA). The results showed that there was a significant main effect for illustration on pupils' achievement in phonics F(1,167) = 24.596, p<0.000; there was non-significant main effect of gender on pupils' achievement in phonics F (1,167) = 0.291, p <0.082; and there was non-significant interaction effect of illustration and gender on pupils' achievement in phonics F (1,167) = 0.253, p <0.615. It was recommended that the Ministries of Education should ensure that textbook authors incorporate children-generated illustrations in the instructional materials for pupils.