The purpose of this study is to compare the efficacy and tolerance of three atypical antipsychotics, which are medications that have been in use for about the last 10 years, in the treatment of psychosis in adolescents. Efficacy refers to how well the medications work in decreasing symptoms associated with schizophrenia, and tolerance refers to the level of side effects and the compliance with taking the medications. All three medications have demonstrated efficacy in treating psychosis without causing extra pyramidal side effects (uncontrolled muscle movements) that are associated with typical, or older antipsychotic medications. Young people may be at a greater risk for side effects from the typical antipsychotic medications. There are studies of the efficacy and tolerance among patients under 18-years-old taking the three drugs in this study: risperidone, olanzapine, and quetiapine. However, at this time there is little data available comparing these three medications. This study is an open-label, random assignment, 12-week study to assess the efficacy and tolerance of these three atypical antipsychotic medications in the treatment of adolescents (ages 12-18) with schizophrenia or psychosis. The participants will be informed of which medication she/he is taking, and will be assigned to the medication randomly (based on chance rather than choice).