Good, and quietly so. Roughly four in five graded settings across the county come in at good or better. The village has its own first schools inside walking distance of most of it. The nearest secondary sits on the hill just above. This is a place people move to for the school run rather than in spite of it.
Ofsted has graded 86 settings across Dorset, the local authority Corfe Mullen belongs to, and 68 of them hold a good or better grade. That is roughly four in five. Two are rated outstanding. Seventeen require improvement and one is rated inadequate, which is a smaller tail than most authorities carry. A further 52 settings have no published grade yet, and they sit outside those counts entirely rather than dragging them down. Those numbers describe the whole county, not the handful of schools a Corfe Mullen family will actually be choosing between, so treat them as the weather rather than the forecast.
The caveat that costs people money is the one about catchments. A school four minutes from your front door is not the same thing as a school your child will be offered a place at. Admissions are run against the local authority's published criteria and each school's own arrangements, and estate agent copy about being "in catchment" is a sales line, not an entitlement. Check the criteria for the specific year of entry before you fall in love with a house, because the arrangement that got the neighbours' children in three years ago is not a promise.
Henbury View First School and Rushcombe First School are the two that serve the village itself, which is the practical answer for anyone with a child under nine and a strong preference for walking. Corfe Hills School is the secondary that most local children move up to, and it is close enough that the older ones will make their own way there and tell you nothing about the day. Queen Elizabeth's School at Wimborne is the other secondary within reach. Beyond the state options, the area is unusually thick with independents, Canford School being the largest of them, which affects the local market in the way independents always do: some families are paying twice, once in fees and once in the house price that got them near the state alternative they are not using. A ring of further first schools sits in the neighbouring villages and Broadstone, so the choice is real rather than nominal.
Grades for individual schools change with each inspection and are published by Ofsted school by school, so look up the current report for any school you are seriously considering rather than trusting a number someone quoted you at a viewing.
Schools are the strongest card Corfe Mullen holds. The state options are close, the county-wide picture is solidly good, and the main risk to a family here is not the quality of the schools but the assumption that living near one is the same as getting into it.