Why would entering tuition paid cause my return to go from 1200 to 200?

[TurboTaxJeffrey · Accepted solution]

Your income likely was in a range that qualified you otherwise for the Working Income Tax Benefit.  However, if you were a full time student for at least 13 weeks of the year, you would be ineligible for this refundable credit...and entering the information from your T2202 would inform the software.

http://www.cra-arc.gc.ca/bnfts/wtb/fq_qlfyng-eng.html#q2