Strategies to provide education cost effectively include deworming children, which costs about 50 cents per child per year and reduces non-attendance from anemia, illness and malnutrition, while being only a twenty-fifth as expensive as increasing school attendance by constructing schools. Schoolgirl absenteeism could be cut in half by simply providing free sanitary towels. Fortification with micronutrients was ranked the most cost effective aid strategy by the Copenhagen Consensus. For example, iodised salt costs 2 to 3 cents per person a year while even moderate iodine deficiency in pregnancy shaves off 10 to 15 IQ points. Paying for school meals is argued to be an efficient strategy in increasing school enrollment, reducing absenteeism and increasing student attention.