Limitations
This study has limitations. At 15 sessions, the sensitivity of our results improved, but our workforce’s power was reduced. The use of methods for imputing missing data preserved the statistical power used to estimate the sample size, and nonresponders were likely to have outliers. Therefore, the loss of these nonresponders could underestimate variability and thus result in an artificially narrow CI for the cognitive training effect. Even if the randomization was homogeneous on the basic eligibility criteria, this would not reflect a potential flaw in the randomization process or a random allocation of severity. The groups born very preterm presented heterogeneity in the severity of their neurodevelopmental profile,At baseline, the intervention group had fewer special educational services. During the training, this frequency was not reported, although this might have influenced the outcome. The neuropsychological assessment was carried out by testers not blinded to the child’s assignment to either the intervention group or the control group; the tester could have given parents suggestions to improve the poor results in the control group, thereby reducing a potential effect of the intervention, or in other ways as if it were an expectancy bias that the intervention should work. However, we found no other options to ensure the feasibility of the study, and testers were asked to adhere to the test guidelines as much as possible.