An elementary school teacher believes that boys are better at math than girls. Therefore, he tends to answer questions for boys while dismissing girls who ask questions. Subsequently boys in his class received higher test scores than girls, which reinforce the belief that boys are better at math than girls. This is an example of:

self-fulfilling prophecy        

Explanation:

Self-fulfilling prophecy: In psychology, the term "self-fulfilling prophecy" is described as one of the different "socio-psychological phenomenon"  in which an individual is ought to expect or predict about something and therefore this expectation or prediction comes out to be true just because he or she believes it that it will happen and therefore his or her resulting behavior would fulfill the given beliefs.

In the question above, the given statement represents the self-fulfilling prophecy.

Luke place the birth of Jesus in Bethlehem.Mary gave birth to Jesus and placed him in a manger “because there was no place for them .