This study involved using a classroom environment questionnaire in North Carolina to assess and improve biology classroom environments and to relate classroom environment to the student outcomes of achievement and attitudes. Part 1 of the study involved 364 Grade 9 and 10 students in Biology 1 at a large comprehensive urban high school in Charlotte, North Carolina. These students completed preferred and actual forms of a modified version of the What Is Happening In this Class? learning environment questionnaire assessing student cohesiveness, teacher support, involvement, investigation, task orientation, cooperation, and equity. Also an eight-item scale from the Test of Science Related Attitudes (TOSRA) was included to measure students' attitudes towards science. Finally, student achievement in biology was assessed using the results of a districtwide achievement test. Analyses of data collected in Part 1 of the study supported the WIHIC's a priori factor structure, internal consistency reliability, discriminant validity and ability to differentiate between the perceptions of students in different classrooms. Investigation of gender and ethnic (black vs non-black) differences in classroom environment revealed no ethnic differences, but there were gender differences for several scales (with boys perceiving more involvement and investigation and less cooperation than girls). / Various analyses of outcome-environment relationships suggested that student achievement is higher in more cohesive classes, whereas student attitudes to science are particularly favourable in investigative, task-oriented and equitable classes. Part 2 involved one class in intervention aimed at improving both classroom environment and student achievement by giving greater emphasis to those features of the learning environment found to be empirically linked to achievement in Part 1. The students involved in the intervention were chosen because they were `at risk' of failing at school. It was found that this intervention involving a cooperative action research plan led to improvement in both classroom environment and achievement for these `at risk' students. Because the methods used in the intervention are lowcost and available to most teachers, they are of wide potential interest to others.