"For my youngest daughter, we had to put her shoes on the radiator all night to get them dry. My house was like a sauna, and that'll put up heating bills."
Another mother, Gem Digby wrote on Facebook that "nobody is arguing about a bit of drizzle" but parents are angry because the children were "left out in downpour" earlier this week.
Ben Carter, the school's executive principal, apologised to parents for not communicating the change in policy to them but urged them to send their children to school with "suitable footwear and a winter coat or jacket."
He defended the "wet play" approach, saying: "Compared with previous generations, children today spend a lot of their time looking at screens and staying indoors. Many have relatively sedentary lifestyles.
"Paradigm Trust academies place great value on outdoor play and exercise as part of children's education and wellbeing. This is why we encourage our pupils to make the most of their time outside during lunch and breaks, even in damp conditions.
"This type of wet play is part of children's normal development. However, in adverse conditions, we will, of course, provide options for pupils to play and be supervised indoors.
"The school has written to all parents and carers to inform them of the policy and ask them to ensure their children have suitable clothing."