First Language Acquisition, Developmental Errors in Vocabulary: A Case Study of a Four -Year- Old Iranian Child

This case study aims to discover the process of first language acquisition of a 4–year-old Iranian child. The focus of the research is on developmental errors the child has created in his language development, i.e. the words which are not correct. To do so, the researcher, during four months, observed and recorded the subject's produced strange words. The recording was done by two ways, Interval recording strategy and event sampling.Developmental errors or strange words are part of the learning process. These words are created due to different reasons. The research shows that during four months and in thirty three records, eleven strange words and expressions were produced. These eleven errors were investigated in this study in details. A table was presented by the researcher in which these errors were thoroughly described.