"I think I've set the next stage of development in motion," he said. "I'm convinced the changes we've introduced are really going to make a difference, a life-changing difference, for children."
He is proud of the introduction of synthetic phonics for all five-year-olds, which has had a mixed response in schools.
"I've no doubt that the phonics approach is right," he said. "I feel we've provided teachers with clear guidance and support."
Mr Wagstaff joined the strategy in January, having worked as senior manager in Ofsted's curriculum division. His new job as deputy director of inspections at Nord Anglia, Manchester, will draw on this experience.
He will be replaced by Pete Dudley, regional director for the East and East Midlands. Mr Wagstaff hopes his successor will continue his policies. "All children, no matter what their background, deserve excellent teaching at all times. We need to ensure they leave primary school with a thirst for learning."
Mr Dudley will act as director until August, in which time he will promote collaboration between primaries. "Individual teachers come up with innovations that work fantastically," he said. "It may just be small things, little ways to engage the children. But if the whole school does it, and other schools do it, it becomes part of our professional knowledge."
He believes his time as a primary teacher in east London, and as primary adviser in Essex, will allow him to keep in touch with what matters most: the pupils.
"By the ages of three or four, children have developed a sense of whether they are an achiever or a failure," he said. "I think that's appalling. The more we can tackle that, the more children will be able to make a contribution. And then the stronger society will grow."