Although language experience is a key factor in successful foreign language (FL) learning, many FL learners fail to achieve performance levels that were predicted on the basis of their FL experience. This retrospective study investigated early cognitive and linguistic correlates of learning English as a foreign language (FL) in a group of Mandarin-speaking elementary students who, at Grade 5, showed discrepancies between actual FL word reading attainment and attainment predicted on the basis of FL experience that had been available to them until Grade 3. Based on the residual score of regressing FL word reading against FL experience at one standard deviation below and above the mean, participants were grouped into overachievers, achievers performing at expected levels, and underachievers. The three cohorts were compared on learner characteristics, including lexical-level (phonological processing and morphological awareness), text-level (syntactic and contextual bootstrapping), and rote word learning abilities measured in Grade 3 and Grade 4. Compared with achievers performing to expectation, underachievers were characterized by poorer performance in lexical-level abilities and rote word learning; overachievers were characterized by one superior lexical-level ability (i.e., morphological awareness) and superior rote word learning. The three groups did not differ in either of the text-level abilities. The results suggest that FL learning can be significantly constrained by limitations in lower level processing capacities in some learners despite adequate FL experience.