 Babies were then tested on the BSID-1 when they were 21 months of age.Mothers level of education, a responsive maternal attitude and 3-month smiling and eye contact was found to predict infant performance on the Mental Scale of the BSID-1, lending support to its validity.While applying the Bayley Scales of Infant Development (BSID-II), it was found that scales may lead to under-estimates of cognitive abilities in infants with Down syndrome.