Government of canada says there is 400$ for every month of full time post secondary school. however, this does not show up on my return. why is that??

quotes from http://www.cra-arc.gc.ca/tx/ndvdls/tpcs/ncm-tx/rtrn/cmpltng/ddctns/lns300-350/323/dctn-eng.html


'Multiply $400 times the number of months indicated in Box C.'