This monograph is a study of how assessment formats and cognitive styles are related to school chemistry. It can help teachers and novice researchers in the field of education to find useful information about: Learning Models, Assessment Formats, Cognitive Styles, Perry Scheme of Intellectual Development. It also gives an insight into the Methodology and Statistics used in educational and social studies. The study explores the relationships between the results of various formats of paper-and-pencil classroom assessments of Chemistry. It also investigates the performance of pupils in different formats of assessment in relation to their cognitive style, personal preferences, and intellectual development. The study was conducted mainly in Greece with the participation of first year upper secondary public school pupils (age 15-16). The result of the study suggests that some of the factors which affect pupils' performance are: the content and presentation of the test, the format of the test, the psychology of the individual.