"Thinking Science," the Cognitive Acceleration through Science Education (CASE) curriculum, is a program designed for 11-14 year olds (in the first two years of secondary school) which encourages them to reflect on their own thinking and to develop their reasoning power in tackling novel problems. This study presents results that represent the first large-scale long-term test of the process of raising standards in schools by concentrating on a thinking skill approach. Overall, about 4,500 pupils in the CASE schools have been featured in the data in this report. Seventeen schools' data have been compared with added-value data from a greater number of control schools. Results indicate that the CASE methodology, even when tried for the first time, produced an average increase on the order of half as much gain in the percentage of pupils obtaining C-grade and above at the GCSE examination (an increase from a National average of 44% to 63% for science in 1996, and an increase from 43% to 57% in science for 1995. In addition, there was the same relative order of increase in achievement in mathematics and a somewhat lower improvement, though still substantial, in English. In schools where teachers had two or more previous years of experience with this approach, the schools more than doubled the proportion of their pupils showing National Curriculum achievement at level six or above in all three subjects. Contains 13 references. (JRH)