Children with autistic symptoms experience challenges in school settings, yet little is known about their academic profiles and the mechanisms underlying the association between autistic symptoms and academic achievement. This study examined the association between autistic symptoms and academic achievement in a population-based sample of children with and without (sub)clinical autism spectrum disorder (ASD). We also investigated potential sex differences and assessed if the association is mediated by vocabulary skills and behavior problems. Information was available for 2038 participants (48.3% boys), and autistic symptoms were assessed using the Social Responsiveness Scale (M = 6.8 years). Diagnosis of ASD was clinically confirmed in 28 children. Academic achievement was determined by a nationwide, standardized test assessed at the end of primary school (M = 11.8 years). Children with more autistic symptoms in early childhood had lower achievement scores in language, mathematics, and world orientation by the end of primary education. There were no sex differences. Furthermore, vocabulary skills and behavior problems partly mediated the association between autistic symptoms and academic achievement. Then, by using propensity matching technique, we compared 140 matched typically developing peers with 28 children diagnosed with ASD. These results indicated no differences in academic achievement between children diagnosed with ASD and their matched typically developing peers. We conclude that autistic symptoms associate with lower academic achievement but by carefully matching on background variables and potential confounders, the academic achievement of children with clinical ASD might not differ from that of their typically developing peers.