This book is based on the observed relationship between science teacher assessment tools and students cognitive development in secondary schools. Four research questions were raised and answered with a hypothesis tested. The population for the study included 130 science teachers, from 20 randomly selected mixed sampled schools. The research questions were analyzed using simple percentages while the hypothesis was tested with the use of Chi-square, at 0.05 significance level. The result of the study showed that the level of question asked during assessment play a significant role in assessing student performance, when high level questions are used in preparing examination questions, the students cognitive development can be ascertained