Yes it is possible in schools, we have done it before. Obviously only works if you have enough spare places to sell. Also the school would need to have it written into the admissions policy stating that places will be available to pay for only if the school has capacity to fulfil the children's needs. This is because a child who has significant special needs might need TA support during their free entitlement. If that same child's parents are paying for extra sessions who would pay for that TA to still be supporting them? The same would happen with a child needing nappy changes. The school would have to allocate staff to do this during the normal entitlement but it would be costly for the whole week. You also have to have the correct ratio of adults to children at lunchtime and therefore staff to supervise dinnertimes.