Background & Objectives: The cognitive processes such as attention, thinking, memory and recall have effective role on the child’s confrontation with daily life problems. The psychological disorders are among those impairments which may severely affect these processes. Researches have shown that schizophrenia can impair children’s cognitive processes to a great extent. The aim of this research was to compare the comprehension, lexical Knowledge, memory and recall in children with schizophrenia, conduct disorder and brain damage.

 Methods: The sample of this causal-comparative research consisted of 80 children (8-13 years old) suffering from schizophrenia, brain damage and conduct disorder as well as a group of healthy ones who were selected from among in and out-patients referring to psychology and neurology wards of Emam Hossein health care center in 2004 (20 subjects in each group). The instruments employed in this research were WISC-R (comprehension, vocabulary, digit span) and Recall Test of Babcoch.

  Results: The one way analysis of variance showed significant differences between the children with schizophrenia, conduct disorder, brain damage and non-patient in comprehension, lexical knowledge, memory and recall (p<0.01). The LSD test showed that comperhension, lexical knowledge, memory and recall in children with schizophrenia were more impaired compared to children with conduct disorder and brain damage. Moreover, comprehension, lexical knowledge and memory in children with conduct disorder were more severely impaired than children with brain damage. However, the recall was better in children with conduct disorder than those with brain damage (p<0.01).

 Conclusion: The results showed that schizophrenic children have comprehension, lexical knowledge, memory and recall more impaired than those suffering from conduct disorder and brain damage. The timely recognition of the cognitive abnormalities seems necessary to have a better diagnosis and choose effective treatment and remedial strategies to cope with them.