Format your letter as a business letter, with the address of the college at the top and justified to the left. Add your address directly underneath this, unless you are writing on letterhead.
Begin with "Dear RHOP,"
State your relationship to the applicant in the first paragraph and how long you have known him.
Give evidence of your ability to properly judge the applicant. More is needed than just such fact as you were his Boy Scout troop leader for four years. Instead, say that over four years you spent at least 400 hours observing the applicant in a variety of circumstances, including his interactions with others, his technology skills and his ability to work in groups and in solo endeavors.
Address the specific concerns of the RHOP program with observed and noted examples. For example, to demonstrate the applicant's sincerity in wanting to become a health practitioner, you might talk about the six years the applicant spent during junior and high school assisting the sports department as a volunteer trainer and conditioning coach. In commenting on the applicant's ability to work with people, it would be proper to discuss when the applicant organized a "trash pick-up day" along the major road leading into town, and how more than 50 people participated because of his efforts and enthusiasm.
Add other important attributes that might tip the decision toward the applicant. For instance, if you are aware that he picks up new concepts and processes much faster than normal students, this would be important to share.
Finish the letter by encouraging the RHOP program to give the applicant an opportunity to be in the program. State that this will be a decision they will never regret.