use of blackboard

I realized the importance of use of blackboard today. Students tended not to listen to what I am talking, but copied the things on blackboard all the time. I wanted to use the previous knowledge in parallel lines to teach them the corresponding angle of congruent triangle. They copied them all. But later, someone asked me why we needed to use parallel lines here=.=

One more, some students even did not know the full name of corr. =.= They said "correct sides, congruent triangles"@@

I know the abilities of students in the class may not be too high. And this lesson was overrun. I will adjust it in later time.