When I enter my current years T2202A it lowers my total refund but when I put in recent year tuition amounts it raises it significantly. Why is it doing this?

[TurboTax-Terry]

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