Praising girls more for the form and appearance of their work, and praising boys more for the content of their work.
Responding more extensively to male students' comments.
Giving boys hints for how to solve problems for themselves, but solving girls' problems for them.
Waiting longer for boys' answers than those of girls.
Folding arms, looking away, or doing other tasks while a girl is speaking.
Rolling eyes over ideas before they are discussed or even fully expressed.