Examples of interventions that yield large long term effect sizes in psychology I was listening to a podcast entitled Very Bad Wizards, hosted by two university academics.  One of the hosts, namely David Pizarro who is a psychologist at Cornell made the claim that most psychological mechanisms have small effects.  I have heard this too mentioned by Daniel Lakens on the small likelihood of psychological effects being very large > d =1.6.  That made me curious.  What are examples of interventions in Psychology that reliably induce long and large changes (large effects that last longer than ~3 months)?  The only example that comes to mind are mood states like trait anxiety being changed nearly indefinitely through CBT with pretty big effects.  A little background, I was a Psychology major and researcher in undergrad.  Enjoy reading about meta research so I can go pretty technical.
Skill acquisition: If you take a novice on a task and get them to practice that task, performance will tend to improve. See the Power Law of Practice. In many cases that I've seen, the difference between between initial and final performance is similar to the standard deviation of individual differences at baseline. So I guess you could call that a d of around 1. Of course, the exact numbers will depend on the domain, but that is indicative.

Of course, you also get forgetting effects which in some sense reduce the effect of skill acquisition over time, but there is also an associated faster relearning effect. And the degree of forgetting is related to a range of factors. In particular, motor-learning seems to have less forgetting than learning related to declarative facts.