Put the goals in some priority order, but be flexible. Guide, don't push. Negative peer group pressure may be counteracted with gently persuasive arguments that point to the adult advantages, financial and social, that reference can get you a good job which in turn can give the adult later on, success, a car and money for good clothes and food, independence and self-respect. It helps if your child's school has a learning environment that is flexible, open, accepting and challenging. Give underachievers the opportunity to work at their area of ability and make sure someone the child respects is available when help is needed.
Isolation is a fine fertilizer for under achievement.
Children who are underachieving should be allowed to study the basics through areas of interest or expertise. At all stages the parents should be involved. If both parents work, it is still possible to form an effective partnership between home and school by communicating after hours. Finally, if only children have the opportunity to establish goals, they would have a much greater chance of fulfilling their potential. Secondary schools for example can offer career and vocational guidance as early as possible.