A randomized placebo-controlled trial of arithmetic training (with the Kumon Method) as an errorless learning method for improvement of cognition in schizophrenia. Outpatients were included after signing an informed consent. The trial consisted of 48 sessions of arithmetic training (twice a week, for 6 months) or placebo (nonspecific recreation, 48 sessions). The patients were evaluated with a neuropsychological battery at baseline, after 6 months (end of intervention) and after 12 months after baseline. The Positive and Negative Syndrome Scale (PANSS) and the Personal and Social Performance scale (PSP) were applied at baseline, after 6 months (end of intervention) and 12 months after baseline. Primary outcome was the performance on three cognitive domains (attention, executive functions and working memory).

Inclusion Criteria:

• Literate (≥5 years of formal education).
• Diagnostic criteria for schizophrenia according to the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, Text Revision (DSM-IV-TR).
• Clinically stable, with constant antipsychotic medication regimen for ≥8 weeks before screening
• No hospitalizations in the last 6 months.

Exclusion Criteria:

• Other Axis I psychiatric disorders, substance abuse or dependence.
• History of head trauma or other neurologic diseases.
• Severe or uncontrolled medical diseases, history of mental retardation or attendance in special-education classes,
• Suicide risk
• Participation in any other kind of psychosocial intervention.