Male Mentoring Program

I want to start a male mentoring program this year for 7th graders. I would like suggestions as to what you feel is most important in a successful male mentoring program to help these students be successful in and out of the classroom. I want to impact academics. But I also want to build character, work on behaviors, increase physical/mental health and prepare them for the future. I feel the group would need to meet once a month. While I would like to open it up to all students, it will probably be most effective if the focus is on 15-25 males. Any thoughts or suggestions you would like to share?