。
Our teacher's really stubborn, isn't he.
Literal
We [of-の] teacher [topic-って] really head [subject-が] hard is [confirmation-よね].
頭が固い ('head is hard') is a set idiom for 'stubborn, inflexible in thinking, closed-minded.' The opposite is 頭が柔らかい ('soft-headed' = open-minded). The って casual topic marker and the final よね (assertion + confirmation-seeking) make this a shared complaint among peers.