Adding teacher's expense credit didn't change return?

[goodglarp]

Prior to entering the teacher's expense credit information, TurboTax showed that I owe around $700 in federal tax. After entering the information to get the credit, the amount I owe was only reduced by about $20. I was expecting the credit to reduce by more. Is this a bug with TurboTax?

[LoganathanB]

Adding the teacher's expenses reduces your taxable income by that number, and the reduction of your tax liability depends on your tax rate on your taxable income.

If the rate is 10% then the tax liability will come down by $25 if the expenses were $250.