What does the word "they" refer to?

Hi~ what do you think the pronoun "they" marked in red refers to?

teachers OR new trends?

Thanks~

It is important to note that many trends last for brief periods in the lives of students
and seldom are identified by them as significant—they come and go
just like fashion trends. Therefore, it is important that teachers stay abreast
of new trends when utilizing this technique, or they might sound dated.