From your button bag select a number of different buttons, two of
each kind. Let the child sort out the pairs and thus become somewhat
familiar with the sizes and shapes. Then mix the buttons, blindfold the
child, and let him match the pairs entirely by feeling. Have him lay
them out in pairs as he matches them. Then take off the blindfold and
let him see them just as he has matched them, and count for himself how
many are right and how many wrong.