What is the meaning of 'reinforce'? and what is the meaning of the whole sentence?
W: How do you always pull off such high grades in English, Harry?
M: I use a computer flash card program to remember the irregular
forms. It makes studying kind of fun.
W: Huh? How does that help?
M: Well, it displays a verb, like “freeze” for example. Then, I have
to type in the simple past and past participle forms.
W: That would be “froze” and “frozen,” right?
M: Right. If I screw up, then it comes up again at the end of my
W: Wow, so it reinforces your shortcomings.
I quite understand why you question its use by W. From the context, it seems that W is confused about its meaning as well! A program that tests you again on something that you got wrong first time around doesn't reinforce anything.
"Reinforce" means what it seems to mean; when you reinforce something you make it stronger. In the area of behavio[u]rism - which is where the verb acquired the relevant meaning - it referred to rewarding the desired behavio[u]r or punishing the behavio[u]r that was not desired, to strengthen (make stronger) the tendency in the subject to do it.