Technology‐based remote research methods are increasingly widespread, including learning assessments in child development and education research. However, little is known about whether technology‐based remote assessments remain as valid and reliable as in‐person assessments. We developed a low‐cost phone‐based language and literacy assessment for primary‐school children in low‐resource communities in rural Côte d'Ivoire using voice calls and SMS. We compared the reliability and validity of this phone‐based assessment to an established in‐person assessment. A total of 685 5th grade children completed language (phonological awareness, vocabulary, language comprehension) and literacy (letter, word, pseudoword, passage reading, and comprehension) tasks in‐person and by phone. Reliability (internal consistency) and predictive validity were high across in‐person and phone‐based tasks. Children's performance across in‐person and phone‐based assessments was moderately to strongly correlated. Phonological awareness and vocabulary skills measured in‐person and by phone significantly predicted in‐person and phone‐based letter, word, and pseudoword reading. Oral language and decoding skills measured in‐person and by phone significantly predicted in‐person and phone‐based passage reading and comprehension. Our phone‐based assessment was a reliable and valid measure of language and reading and feasible for low‐resource settings. Low‐cost technologies offer significant potential to measure children's learning remotely, increasing the inclusion of remote and low‐resource populations in education research.