7th Period is a Secret (Manga)

From Serenus Dreamers: Shun is a girl who used to be shy and gloomy. Wanting to change, she transforms herself into a bright girl when her family transfers into a new place. Hoping to fit in, she laughs and smile at everything agreeing with everyone. She starts to fear that her young teacher is seeing right through her. Is she just imagining, or is it true---?