This is not an easy question to answer without knowing more specifics about the teenagers involved. For those kids who do not have a supportive parent, it will be important for them to find role models in other adults. Some cities have mentoring programs or big brother/big sister programs where the teen is paired with an adult volunteer. Bring in young adult or older teen speakers who have been through tough times but overcame them in spite of the odds.
Teachers can motivate the kids to learn and do well by having a motivational learning system in place where students earn things that the teacher can control. This can be achieved through giving rewards or incentives for doing their work on time or getting a good grade, or improving their performance.
You can help the teens identify their strengths and interests, and then give them opportunities to experience what they love to do. For many kids, if they have at least one hobby or activity they enjoy, such as music, sports, or church, it helps motivate them to do better in other areas of their lives.
Thank you for reaching out and caring for children!