Can teachers tell sometimes if a boy likes a girl in class?

-Speaking as a teacher, generally yes - it's pretty obvious. We see the stolen glances, the staring when one thinks the other isn't looking, the longing looks, the passed notes, the shy smiles, all of it. Don't worry though, we see it all the time and it's not like it occupies a lot of our thoughts - it's just a little love in the air, that's all. :)Teachers are much more aware of what goes on and the dynamics between students than a lot of students are aware of. A lot of times students aren't very subtle about their crushes, they stand out a lot of times.
Probably, it depends how old the group of students are. Most of the time though they will be able to tell because of flirting and if the student is getting of task in class. So, i would say yes about 95% of the time.
Yes, i do feel so. Teachers can really really observe more than we can think. Once they hav doubt on someone, they may start noticing even more carefully... It may lead to a really awkward situation...
hahah ohhhh yeah. trust me. it can be REALLY embarassing.
Yes I am a teacher and I see it all the time! :)
yes, chance is about 70%.