I am having the same issue. 

I was able to enter the amount when I went back to the education summary page and edited that student. 

I am having the same problem, hope someone has found the solution.

Go through the entire education interview until you reach a screen titled "Your Education Expenses Summary".  Click edit next to the student's name. That should take you to a screen “Here’s your Education Summary”. Click edit next to the section you want to change; tuition, in your case (click edit next to the school name).

I'm having the same issue, I was able to enter the info but on the screen where it shows the summary, it shows the amount from last year and zero for this year, just makes me wonder if this section even works - especially because I get exactly zero tax credit for spending $40k on my son's college