I need to determine if an intervention had an effect. In the experimental design, measures were taken at three points in time: pre-test, post-test #1 and post-test #2. One group (group A) received the intervention between pre-test and post-test #1. The other group (group B) received it between post-test #1 and post-test #2. Thus, both groups served as control at different points in time.
In other words, the experimental design can be summarised as follow:
Group A: pre-test -> treatment -> post-test #1 -> no treatment -> post-test #2
Group B: pre-test -> no treatment -> post-test #1 -> treatment -> post-test #2
The expected effect is that group A will progress between pre-test and post-test #1, and will maintain its gain at post-test #2. However, group B, having only underwent the intervention between post-test #1 and post-test 2, will remain stable between pre-test and post-test #1, but will progress between post-test #1 and post-test #2.
Given these conditions, which statistical tests can I use? I have seen repeated measures ANOVA being recommended but all the use case examples I have seen involved two or more different treatments being administrated in different orders, which is not the case here, unless "no treatment" can be regarded as a kind of treatment (which I am not sure of).