Testing can enhance memory, but what is the optimal placement of tests during a learning episode? Two potential placements are having short interim tests administered throughout learning or a single longer test at the end. The grain size hypothesis stipulates that interim testing should result in better reten- tion at final cumulative assessment as retrieval success during prac- tice is expected to be higher. However, previous research has found that although interim tests result in better practice performance, this does not translate into an advantage at cumulative assessment. We evaluated the grain size hypothesis using lists of related and unre- lated words and exposure-matched restudy controls. We also assessed whether the benefit of interim tests on cumulative assessment was dependent on the format of cumulative tests. Interim tests enhanced both practice and cumulative assessment performance and this was not dependent on test format. A meta-analysis of the extant litera- ture also found a large practice test effect and a smaller, but still sig- nificant, cumulative assessment effect, in line with the grain size hypothesis.