Nice to see you little cheer leaders are following this closely. Hello cheerleaders.
And I would argue it is not relevant, because the provision exists, it is a matter of not taking up the provision. At 5 the provision has to exist because the child exists, if the parent decide to pay for schooling elsewhere that provision is not lost it is still there. The fixed costs remain the same, the marginal costs of one less pupil per classroom is negligible and the variable costs are unaffected unless you feel the output of one less pupil will significantly increase the output/results of the other 29, based on a 30 kid classroom.
So I refute your argument that it reduces the burden on the state, because the obligation stands. If a child's parents suddenly go bankrupt, the child would not go uneducated because the provision for a state education exists for that child.