Arithmetic fluency and number processing skills in identifying students with mathematical learning disabilities

Background: Students with mathematical learning disabilities (MLD) struggle with number processing skills (e.g., enumeration and number comparison) and arithmetic fluency. Traditionally, MLD is identified based on arithmetic fluency. However, number processing skills are suggested to differentiate low achievement (LA) from MLD. Aims: This study investigated the accuracy of number processing skills in identifying students with MLD and LA, based on arithmetic fluency, and whether the classification ability of number processing skills varied as a function of grade level. Methods and procedures: The participants were 18,405 students (girls = 9080) from Grades 3–9 (ages 9–15). Students’ basic numerical skills were assessed with an online dyscalculia screener (Functional Numeracy Assessment –Dyscalculia Battery, FUNA-DB), which included number processing and arithmetic fluency as two factors. Outcomes and results: Confirmatory factor analyses supported a two-factor structure of FUNA-DB. The two-factor structure was invariant across language groups, gender, and grade levels. Receiver operating characteristics curve analyses indicated that number processing skills are a fair classifier of MLD and LA status across grade levels. The classification accuracy of number processing skills was better when predicting MLD (cut-off < 5 %) compared to LA (cut-off < 25 %). Conclusions and implications: Results highlight the need to measure both number processing and arithmetic fluency when identifying students with MLD.