Explanations for the unexpected findings

a) The length of the spacing interval. In their study, Goossens et al. compared different lengths of spacing, i.e., a short spacing and longer one. Previous research has shown that there seems to be an interaction between length of spacing and the length of the interval between the last study session and the final test, i.e. the test interval (5). Thus, for a given test interval, there appears to be an optimal spacing between two learning sessions. For example, for vocabulary learning the optimal spacing for a final test taking place in a week is 1 day (5). In light of these previous findings, it is possible that the short spacing conditions were more adequate for most of the test intervals used (1 day to 2 weeks). What about the long test interval of 11 weeks? Here one would expect long spacing to outperform short spacing. However, one needs to consider that the two spacing conditions used are not extremely different from each other – distributing of studying within one week versus two weeks. It may well be that if one increased the spacing further to create a more extended learning schedule, one would start finding differences in the long term on memory performance.

b) No real restudy only versus retrieval only condition. In order to be as authentic as possible, the authors decided not to have a pure restudy only condition and a retrieval only condition. In all conditions, pupils engaged in exercises that required them to retrieve information from memory at some point during studying. Thus, in contrast to most laboratory studies, the difference between the retrieval practice condition and the restudy condition was much more subtle here. Plus, all pupils engaged in a range of different types of exercises to learn the new vocabulary. This variability in learning may have contributed positively to the overall performance in all conditions – thereby, diluting the effects of restudy versus retrieval.

c) Retrieval exercises too challenging for young pupils. For the younger pupils (grades 2 and 3), the restudy strategy actually outperformed retrieval practice. This is a finding worth looking further into: Could it be that retrieval practice is more beneficial for older kids? Inspecting the memory performance on the retrieval practice exercises in grade 2 children tells us that their performance is lower than that of older children in higher grades. This resonates well with another applied classroom study (3) that clearly showed that younger kids may need more scaffolding during retrieval practice exercises for it to be effective. Goossens et al. mention that children may have focused more on the restudy exercises compared to the retrieval exercises because retrieving the description of new vocabulary from memory may have been too challenging. They report that often blank retrieval sheets were returned. Again, additional scaffolding of the retrieval process could have increased the success of this strategy tremendously.