Bobby did not learn to read until he was an adolescent. When he did learn to read it was much harder for him to learn and it took him longer to learn to read. If Bobby had learned to read during the early childhood years into the middle childhood years he would have had an easier time learning to read. Bobby had a hard time learning to read because he did not learn to do so during the _____ period.
You are asking for the period when a child is younger and still learning basic things, such as reading, these things are usually taught or learned during the early childhood period.
