Frequently, I will receive a referral from another therapist when they have been asked to see a second member of the same family. A Systemically trained therapist would not do that. During my 2000 hour internship, my training was focused on helping the entire system, which means helping the entire family and the dynamics in that family.
When we are in a family, every behavior one member of the family participates in effects all of the other family members. When parents expect to drop off a young person with a therapist without recognizing the importance of actively participating themselves, they are exhibiting what might be considered an unrealistic expectation of success. A good therapist can help a young person develop some healthy social skills, but the most important success will be evident when the therapist and the parents are reinforcing an agreed-upon set of structures for the family setting.