The research reported in this article makes two distinctive contributions to the field of classroom environment research. First, because existing instruments are unsuitable for science laboratory classes, the Science Laboratory Environment Inventory (SLEI) was developed and validated. Second, a new Personal form of the SLEI (involving a student's perceptions of his or her own role within the class) was developed and validated in conjunction with the conventional Class form (involving a student's perceptions of the class as a whole), and its usefulness was investigated. The instrument was cross-nationally fieldtested with 5,447 students in 269 senior high school and university classes in six countries, and cross-validated with 1,594 senior high school students in 92 classes in Australia. Each SLEI scale exhibited satisfactory internal consistency reliability, discriminant validity, and factorial validity, and differentiated between the perceptions of students in different classes. A variety of applications with the new instrument furnished evidence about its usefulness and revealed that science laboratory classes are dominated by closed-ended activities; mean scores obtained on the Class form were consistently somewhat more favorable than on the corresponding Personal form; females generally held more favorable perceptions than males, but these differences were somewhat larger for the Personal form than the Class form; associations existed between attitudinal outcomes and laboratory environment dimensions; and the Class and Personal forms of the SLEI each accounted for unique variance in student outcomes which was independent of that accounted for by the other form.