Conversion therapy rarely uses physical techniques like Anderson described suffering. And even in his case, the hot water poured over him was meant to startle him, not to cause significant pain, which as you rightly presume would trigger criminal/civil consequences independent of bans on conversion therapy.
The harm of conversion therapy lies rather in the inevitable consequences of the combinations of spiritual/psychological counseling techniques that promise to reduce or eliminate "unwanted same-sex attraction."
Such promises cannot be met, which is one of the reasons that youth who willingly participate in conversion therapy suffer more harm than youth who are coerced.
One organization that operates in Missouri offering to train church members and church-school staff in administering such "therapy" is Living Streams/Desert Waters Ministries. They are careful to avoid physical punishment or physical aversion techniques in their practices. (Although, youth who have come out of Living Waters programs recently report that some self-administered physical aversion practices are still encouraged - like children snapping rubber bands worn on their wrists or pinching themselves if thoughts of same-sex attraction arise.)
But this is not something that would trigger social services intervention or rise to the level of a crime unless the practice of attempting to change a child's sexual orientation were itself against the law.
What's critical to remember here is that very good evidence shows that it's the attempt to change orientation that causes the mental health distress and high suicide rates associated with conversion therapy - not physical torture, whether or not physical torture takes place.
Stats? This isn't something churches and church schools keep records on. We have no good way to know how many young people undergo this "therapy" in the Kansas City Metro area.
We do know that queer young people in the area report undergoing the therapy either by coercion or voluntarily. We also know that churches and church schools are fiercely lobbying against laws to criminalize the practice.
