Letters of Recommendation Format?

Hello,

I am helping my son obtain 3 letters of recommendation from people he knows. One of the common questions they ask us is "what format do they want it in?" I know they want people who know him well, and they do, but people are not sure what they should write or areas they should focus on.

Are there any "sample" letters of recommendation I could forward to them to help them get a start?

Any help would be greatly appreciated.

Thanks!