Send them to Peter Leftkowitz's training. They will learn both sourcing and recruiting, great foundation on how to really recruit, not just surf the job boards, phone sourcing, deep interviewing, client development, all of it. It's not cheap, but it's comprehensive and worth it. www.morgancg.com
As a sourcer I like to consider my role as a "researcher" because I spend on average 3-4 hours per day researching trends, competitors, markets to flush out candidates for my business partners and retrieving information from the Internet. When I stepped into my role 3 years ago I was entering a new industry (6 years in the health services industry to financial services). First I needed to understand business acrumen, Hoshin plans and study business plans so I knew how best to support my business partners in achieving their goals. I tapped into internal learning portals and attended alot of internal meetings. I'm still involved in those meetings. Secondly, I reached out and formed an alliance with others in the industry to obtain a better understanding of industry trends. I took the initiative to enroll in professional media (like this site) to expand my soft skills. Specifically, I wanted to learn more about research techniques using the Internet. Contributors to sites like this one, ERE.net and Jim Stroud's Recruiters Lounge produce some very valuable and specific topics.
What is it you want them to learn first? Research skills? Internet or Telephone?