Cumulative assessment refers to interspersed testing in which each assessment covers all previous content and the mean assessments' grade weighs in for the final exam grade. The effect of cumulative assessment on motivation and performance might differ between summative (i.e. assessment grades weigh in for the final exam grade) and formative (i.e. the assessments grades do not weigh in) variants. The present study explored this hypothesis in two field experiments in a higher education course (Exp 1: n = 102; Exp 2: n = 88). Each experiment used a single-factor, between-subjects design with type of cumulative assessment (i.e. summative vs formative) as independent variable and motivation (Exp 1: self-study time, topic interest, perceived competence; Exp 2: preparation time and self-efficacy) and performance (Exp 2: cumulative assessment performance; Exp1 and Exp2: final exam grade and delayed test performance) as dependent variables. The results of both experiments reinforced each other. In the summative condition, the final exam grade was higher than in the formative condition. However, when the summative assessments were discarded from the final grade, this difference disappeared. Also, in both experiments, the conditions did not differ on motivation measures. Theoretical and practical implications of our findings are discussed.