This paper describes the mixed methodology evaluation of the Own-Voice Intensive Phonics (OVIP) programme with 33 secondary students with persistent literacy difficulties. The evaluation involved a quasi-experimental evaluation in which 33 students in years 7-9 in four schools used OVIP over an 8 week period and were monitored at three times for their word reading, phonic decoding and phonological skills. Students, teaching assistants and teachers involved were also interviewed about the use of OVIP, the perceived processes and outcomes. Assessment results showed that OVIP was associated with greater gains in word reading than these students' usual teaching/intervention approaches. Those interviewed also experienced benefits associated with using OVIP. It was further found that word reading gains were not related to a measure of being at risk of significant literacy difficulties. Participants identified the use of their own voice, the student's agency and working at their own pace as key factors relevant to how OVIP worked. These factors aligned with a working OVIP programme theory. The findings are discussed in terms of further development and research related to an own voice approach to addressing persistent literacy difficulties.