Language learning beliefs are considered to be an important factor influencing student learning outcomes. This mixed-methods research investigated English language learning beliefs of Iranian English language learners. Data were collected from 226 junior and senior male and female high school students using the Beliefs about Language Learning Inventory (BALLI) and semi-structured interviews. Participants reported strong beliefs in terms of 'motivation and expectation' and 'foreign language aptitude'. First and third graders' mean belief scores were statistically different across their 'overall beliefs', 'foreign language aptitude', and 'motivation and expectations'. Moreover, although the overall gender differences were not statistically meaningful, significant differences were noticed with regards to beliefs about 'difficulty of language learning' and 'foreign language aptitude'. The results underscore the hypothesis that changes in language learning beliefs happen due to learners' stage of development, i.e. their grade. Further, certain misconceptions among high school learners were noticed about the role of aptitude and intelligence, error correction, and supremacy of learning certain forms of language. The implications are discussed with reference to language education and policy development.