Southwick's schools do not currently carry a published Ofsted grade in the local picture, which is a data limit rather than a verdict on the schools themselves. That said, the shape is clear enough. More than a dozen primary schools sit within a reasonable school run across Southwick and its immediate neighbours. Two named secondaries handle most of the year 7 to 11 population within a drive. It is not a school-chase town, and it is not a school-crisis town either.
Names on a map do not guarantee names on your admission letter. The primary pool across Southwick and its neighbours runs through Glebe Primary School, Buckingham Park Primary School, Eastbrook Primary Academy, Holmbush Primary Academy, Swiss Gardens Primary School, Mile Oak Primary School, Benfield Primary School, Brackenbury Primary School, Peter Gladwin Primary School and Shoreham Beach Primary School on the maintained side, with St Mary's Catholic Primary School and St Peter's Catholic Primary School covering the Catholic option. That is enough choice that a family with a car and a normal appetite for the school run has real options. Which of them will actually take your child depends on the year, the applications, the sibling policy, and the distance formula the admissions team is using this cycle. Nobody in Southwick has beaten that algorithm yet, and nobody is going to. If a specific school matters, the school office and the West Sussex admissions team are the source of truth, not the address you have your eye on and not the Wikipedia page you have already read. At the secondary end, Shoreham Academy and Portslade Aldridge Community Academy handle most of the year 7 to 11 catchment, both slightly out of town but the sort of drive that coastal families take as normal. The independent option is Shoreham College. Specialist provision runs through Herons Dale School and Hill Park School, and Hove Micro-School sits in the pool for families looking for something outside the usual pattern. None of these schools shows a current Ofsted grade in the local data behind this page. This answer will not pretend to rank them for you. If grades matter, the Ofsted register itself is where you go, and the grade you find there will be more recent than any generated summary about a coastal town.
Three out of five is the honest verdict. Enough schools to choose between at the primary end, thinner at the secondary end, no local grade data to lift the score or drop it. A normal-shaped school landscape for a coastal town where the schools are one of the many things you will end up handling rather than the one thing you moved for.