The WISC-V is one of the most used instruments in clinical assessment. The Full Scale IQ (FSIQ) and the five primary index scores are used for individual decisions and predictions. Thus, the stability of these scores across time is crucial. The five index scores are the Verbal Comprehension Index (VCI), the Visual Spatial Index (VSI), the Fluid Reasoning Index (FRI), the Working Memory Index (WMI) and the Processing Speed Index (PSI).

The aim of this study was to investigate the long-term stability (interval >1 year) of the French WISC-V scores. 63 Swiss children were assessed twice, using a 1.44 year interval.

The mean difference results (t-tests, Cohen’s d) indicated small (FSIQ, VCI, VSI, FRI) to trivial (WMI, PSI) effect sizes, suggesting none or small increase of performance after more than one year.

For the stability coefficients (test-retest correlations), only the VSI (.86) and PSI (.85) were stable enough for clinical individual decisions; the other scores were too low for confident individual decisions (<.80).

Regarding the intra-individual stability, less than half of the children demonstrated stable intra-individual performance (performance was stable if it was within a confidence interval of ±2 standard errors of measurement).

Our results suggest that the VSI and PSI scores are sufficiently stable for clinical decision. Surprisingly, the FSIQ is less stable than these two index scores. These long-term stability results suggest an interpretation of the scores in the “here and now”. Nevertheless, the interpretation of our results should be taken with caution, given the small sample size.