The testing effect occurs when students, given information to learn and then practice during a test, perform better on a subsequent content post-test than students who restudy the information as a substitute for the practice test. The effect is often weaker or reversed if immediate rather than delayed post-tests are used. The weakening may be due to differential working memory resource depletion on immediate post-tests with resource recovery due to rest following a delayed post-test. In three experiments, we compared an immediate post-test with a 1-week delayed post-test. Experiment 1 required the students to construct a puzzle poem and found working memory resource depletion occurred immediately after learning compared to a delay. Experiment 2 using text-based material tapping lower element interactivity information and experiment 3, again using a puzzle poem, compared study-only with the study and test groups. A disordinal interaction was obtained in both experiments with the study-only groups superior to the study--test groups on immediate content post-tests and reverse results on delayed tests. Working memory capacity tests indicated a non-significant increase in capacity after a delay compared to immediately after learning with medium size effects, but in experiment 2, there were no working memory differences between the study-only and the study and test groups. Experiment 3 increased element interactivity and found an increased memory capacity for the study-only group compared to the study and test group with the immediate test contributing more of the difference than the delayed test. It was concluded that increased working memory depletion immediately following learning with a test contributes to the failure to obtain a testing effect using immediate tests.