A Calgary volunteer coach at Henry Wise Wood High School has been charged with sexual assault after police allege he groomed and abused a teenage girl over nearly two years.The Calgary Police Service said officers received a complaint on May 12 alleging a minor had been sexually abused by a volunteer coach connected to the school and extracurricular activities.Police allege the suspect met the girl when she was 15 years old and used his position of trust and authority to groom her before the assaults began.The CPS Child Abuse Unit launched an investigation and arrested the suspect the following day.Drew Alan Robertson, 50, of Calgary, has been charged with one count each of sexual assault, sexual exploitation and making sexually explicit material available to children. He is scheduled to appear in court on May 20.Investigators said the victim is receiving support through the Luna Child and Youth Advocacy Centre.“Coaches are supposed to be instructors, leaders and mentors,” Staff Sgt. Chris Tudor of the CPS Child Abuse Unit said in a statement. “Sexual exploitation by a person in a position of authority is a betrayal of those values, and offenders must be held accountable.”Police said the Child Abuse Unit operates in partnership with the advocacy centre to provide what they described as a child-focused and trauma-informed response to abuse investigations.The CPS is asking anyone who may have information about similar incidents, or who believes they may have been victimized, to contact police at 403-266-1234 or submit anonymous tips through Crime Stoppers Calgary.