Archives of Disease in Childhood reports that children less than 18 years of age with chronic fatigue syndrome/myalgic encephalopathy have high rates of absenteeism.  These researchers concluded that decreased attendance was due to reduced physical function or pain rather than anxiety. 

Reference:  Crawley, Esther, Sterne, Jonathan

Association between school absence and physical function in paediatric CFS/ME Arch Dis Child 2008 0: adc.2008.143537