It should be specified in the maintenance order, if there is one. It varies. Mine was up to the age of 23 while still in full time education. Not sure what the defintition of full time education is. My wifes ex was up to the age of 16 but he continued to contribute informally through university. No there is not a reduction but either party can have it reassessed (up or down!). However, university can be expensive when you take into account accommodation. Best to come to an informal arrangement if you can. They dont need to live at home either.