Answer:A self-fulfilling prophecy
Step-by-step explanation:
A self-fulfilling prophecy is based on how we can tend to believe that something is going to be true and as a result we start to act as if it has happened already cause we believe it's true.
What we expect sometimes shapes how we act towards it and which will affect the view of others about us such as when we expect to fail we start acting like we have failed already then people begin to see is as failures. People will start to say the same thing to us and in our mind this will reinforce what we already believe and expect.
Remedial classes are usually catered for students who aren't doing good in that subject hence it is likely that Diana already believes that she is not good in maths so when the teacher said he doesn't expect her to do good it reinforced her original belief of not being good in maths hence he start to not study because she feels she has already failed ;this is referred to as a self fulfilling prophecy.