Currently, UK state education is funded via income tax. Parents of children who do not attend state school, e.g. because of independent schooling, home schooling etc, should therefore be able to deduct their expenses for schooling from their income tax.
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While middle income families are already disadvantaged in terms of disposable income vis a vis childless households, it would be fair to allow them to tax deduct any extra schooling expenses on top of what they already fund through their income tax. This would then allow a broader group of households to benefit from a wider choice of schooling options while encouraging schools to compete for the brightest students.