Actually, stimulants can affect growth velocity, but the mechanism for why this occurs is not known definitively (although there are a lot of theories). In addition, it is not known if children who take stimulants eventually catch up to their expected height.
Here's a link to a clinical review article on this topic:
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2408826&tool=pmcentrez