"It was very hard to move to the next level of Becky's learning without really knowing what she had understood," Darroch said.
"I saw a video of the RPM technique ... and it was a 'lightbulb moment'. The idea that she could have a paragraph in her head but could only speak two words was amazing.
"We've started off ... with simple questions and answers, but I can already see more confidence in Becky, and I have more confidence in her."
Darroch went to an RPM workshop by Vosseller in Sydney in April 2015 with Annette O'Brien, the Orewa mother of autistic boy Declan, 13.
Astounded by what they witnessed, the women researched the technique further and gathered support from families to bring Vosseller to New Zealand.
"What I like about RPM is that it accesses the child where they are at now," Darroch said.
"I realised it wasn't about giving up on trying to improve Becky's speech, it was about letting her talk now.
"The youngest at the April workshop was 6 and the oldest was 22 ... but all the parents left with new perspectives on their kids."
O'Brien's son, Declan, was diagnosed with autism when he was 2. She began homeschooling him recently because he was becoming frustrated at school.
"[With] autism, your brain and body have a disconnect. He was learning below his level because, though he was understanding the information, he didn't have the motor skills of speech to communicate that he could.
"Now, I'm able to teach him age-appropriate content. Like everyone his age, he's not always keen on his lessons but once his brain is engaged, his body calms down and he can answer basic questions on the letter board to show his understanding."
Autism New Zealand national education manager Neil Stuart was aware of RPM but was unsure of its efficacy.
"There are hundreds of techniques for children with autism. I don't believe there's a single technique that works for all children.
"I haven't seen any evidence for [RPM] so I can't endorse it. My advice to parents who are curious about it is to see where the research is."
Darroch and O'Brien have organised further, already sold-out RPM workshops for September and November, to be run by American RPM practitioner Erika Anderson.