Based on your
employment earnings the software calculated your entitlement to the
"Working Income Tax Benefit" however the government disallows this
benefit to students so entering the T2202a 'Tuition Certificate' caused a
recalculation and removal of this amount from your refund.
You are not eligible
for the WITB if:
You do not have an
eligible dependant and are enrolled as a full-time student at a designated
educational institution for more than 13 weeks in the year;
Ultimately you will
receive a bigger tax benefit from your tuition this year or in a future year as
a carry forward deduction or by transferring the credit to a parent now.
http://www.cra-arc.gc.ca/bnfts/wtb/fq_qlfyng-eng.html