A common concern raised by teachers from secondary schools and junior colleges in Singapore is the apparent inability or reluctance of adolescents to think critically and originally. Adolescent thought processes are probably shaped by the change in intellectual pace and quality between the primary and secondary school curriculum. This study of adolescent thinking considers the last two Piagetian states of cognitive development and the transition from concrete operations to formal operations, focussing on the adolescents' ability to make judgements and the extent to which adolescent judgement is guided by possibilities other than those given. A sample of 800 adolescents from 13 to 16 years of age was drawn from 6 schools. Subjects were asked to respond to the Test of Judgmental Ability, an anecdotal measure. The cross-sectional study revealed developmental differences in performances between adolescent males and females in favor of males, particularly at higher levels of judgement. Various analyses showed that age is the dominant factor accounting for differences in judgmental level, with academic achievement and home environment as contributing factors. Results suggest a transition period between the two forms of thinking. (WP)