Examples of interventions that yield large long term effect sizes in psychology
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.