as with the nfp programme the stimulation programme improved internalising behaviour walker et al the stimulation intervention also improved earnings by at age gertler et al the perry preschool programme enriched the lives of and yearold lowincome black children with initial iqs below at age three they attended twoandahalfhours of centrebased preschool five days a week for two years in addition home visits promoted parentchild relationships the programme ended after two years of enrolment and both treatment and control groups entered the same school