From an evolutionary perspective, the long period of childhood exists so children can learn and experiment in a relatively pressure-free environment. Most social scientists refer to this pressure-free experimentation as play (e.g., see Groos, 1901), although Montessori preferred to call this activity the work of childhood. Children certainly are serious when engaged in the kind of play that meets developmental needs and, given freedom and time, will choose purposeful activities over frivolous make-believe ones.