The current study investigated the development of children's performance on tasks that have been suggested to underlie early mathematics skills, including measures of cardinality, ordinality, and intelligence. Eighty-seven children were tested in their first (T1) and second (T2) school year (at ages 5 and 6). Children's performance on all tasks…

First-order theory of mind (ToM) development has shown to conform to a Guttman scale, with desire reasoning developing before belief reasoning. There have been attempts to test for internal consistency and scalability in advanced ToM, but not over a broad age range and only with a limited set of tasks. This 2-year longitudinal study (N = 155;…

Children start preschool with large individual differences in their early numerical abilities. Little is known about the importance of heterogeneous patterns that exist within these individual differences. A person-centered analytic approach might be helpful to unravel these patterns and the cognitive and environmental factors that are associated…

Research has indicated age-related improvements in relational binding, an important process of episodic memory, across development. However, little research has focused on individual differences in relational binding and factors contributing to this variation. Although differences may arise from various sources, early caregiving has been shown to…

The stability of callous-unemotional (CU) traits and both individual and contextual factors that influence this stability have been studied in community adolescent samples but not to great extent in adolescents who have been arrested. We estimated the developmental changes in CU traits measured over the course of 36 months (6-month intervals)…

In order to understand variability in second language (L2) acquisition, this study addressed how individual differences in cognitive abilities may contribute to development for learners in different contexts. Specifically, we report the results of two short-term longitudinal studies aimed at examining the role of cognitive abilities in accounting…

Most of the individual difference variance in the population is found "within" families, yet studying the processes causing this variation is difficult due to confounds between genetic and nongenetic influences. Quasi-experiments can be used to test hypotheses regarding environment exposure (e.g., timing, duration) while controlling for…

The aim of the current study was to examine different aspects of procedural memory in young adults who varied with regard to their language abilities. We selected a sample of procedural memory tasks, each of which represented a unique type of procedural learning, and has been linked, at least partially, to the functionality of the corticostriatal…

Models of irregular word reading that take into account both child- and word-level predictors have not been evaluated in typically developing children and children with reading difficulty (RD). The purpose of the present study was to model individual differences in irregular word reading ability among 5th grade children (N = 170), oversampled for…

Across multiple schools and sites, the impact of grade-at-intervention was evaluated for children at risk or meeting criteria for reading disabilities. A multiple-component reading intervention with demonstrated efficacy was offered to small groups of children in 1st, 2nd, or 3rd grade. In a quasi-experimental design, 172 children received the…

Multilevel modeling was used to address the longitudinal stability of standard scores (SSs) measuring intellectual ability for children with Williams syndrome (WS). Participants were 40 children with genetically confirmed WS who completed the Kaufman Brief Intelligence Test--Second Edition (KBIT-2; A. S. Kaufman & N. L. Kaufman, 2004) 4-7…

In this article, I describe studies conducted over 25 years with secondary and post-secondary L2 learners in the United States. The evidence from these studies shows that there are important connections between students' early L1 skills and their L2 aptitude and L2 proficiency and that individual differences in students' L1 skills in elementary…

Participants in a longitudinal study, selected according to Stanford-Binet Intelligence Test scores administered in the 1930s, and their occupations, took the Wechsler Adult Intelligence Scale. Data suggest persons increase in mental abilities over time while maintaining IQ positions relative to peers. Changes in IQ are not related to occupational…

Mathematics achievement differences among sixth-graders were analyzed in a four-wave design and explained by aptitude and instructional variables in a structural equation framework. The results demonstrate the local nature of achievement models in that neither their measurement nor structural components proved generalizable across two groups of…