Intelligence is determined by both heredity and environment. Children learn concepts and the words for those concepts in stages. Learning methods include incidental, trial-and-error, imitation, and directed learning. There are seven areas of intellectual activity. Children's learning can be guided by adults. Caregivers can encourage reading and math readiness during play and everyday activities. Toys should be safe, appealing, and appropriate to a child's age. Speech difficulties include problems with articulation and stuttering.