Vocational, academic, and special education teachers who had received inservice education in the individualization of instruction were observed to determine the effect of the education on their teaching. Data collection and conversion instruments were developed. Six trained observers performed 364 classroom observations in 10 Texas districts with inservice programs, and in 10 without; the 10 inservice program administrators were interviewed. A literature review indicated that certain methods of inservice instruction rated higher in implementation than others (laboratory, simulation, team research, and internship), suggesting seven hypotheses which were tested, using linear regression analysis. Four examined inservice education's relationship to teacher performance; three focused on the degree and level of individualization performed by each of the three groups of teachers. Inservice education in individualized instruction was found to make a difference for academic teachers, and, to some extent, for special education teachers, but not for vocational teachers. This suggests that teacher classification differences should be considered in planning inservice education programs. Academic teachers in Texas apparently are not receiving adequate training in individualization from teacher education programs, but the Texas vocational certification program is apparently producing teachers who can individualize instruction. Inservice instruction methods made no significant difference. The instruments are appended. (AJ)