"We find that the relationship between firm size and employment growth is sensitive to these issues. However, our main finding is that once we control for firm age there is no systematic relationship between firm size and growth."
http://econweb.umd.edu/~haltiwan/size_age_paper_R&R_Aug_16_2...
EDIT:
I should say that it's not that small businesses don't create jobs, it's just a particular type of small business (young ones) that create most of them.
Additional discussion - http://www.richmondfed.org/publications/research/econ_focus/...