Purpose: The purpose of this study was to examine the relationship between parent concerns about children's oral language, reading, and related skills and their children's performance on standardized assessments of language and reading, with a particular focus on whether those relationships differed between children recruited for in-school versus online participation. Method: This study used data from a larger, longitudinal project focused on children with and without developmental language disorder (DLD) and/or dyslexia. The "in-school" sample (n = 133) completed assessments in-person before school closures, and the "online" sample (n = 84) recruited via advertisements completed assessments online. Parents completed a checklist of concerns. All children completed norm-referenced assessments of language and reading. Results: The two recruitment strategies yielded samples that differed in racial diversity (higher in the in-school sample), caregiver education levels (higher in the online sample), and word reading test scores (higher in the online sample). Parents in both samples reported higher levels of concerns about literacy skills than oral language skills, and the correlation between parent concerns about literacy and children's word reading test scores was stronger than the correlation between parent concerns about oral language and children's language test scores. Conclusions: Researchers and clinicians should be aware of how recruitment strategies and assessment modalities (e.g., in-person vs. tele-assessment) may impact participation in studies and clinical service. A reliance on parent concerns about oral language to prompt a language evaluation may contribute to low rates of identification of children who meet criteria for DLD. Future research can consider parent concerns about literacy, attention, and executive functions as indicators of a need for language evaluation, especially considering the high comorbidity between language and other developmental disorders.