Lǎoshī méi lái shàngkè, xuésheng zhǐhǎo fàngyáng le.
The teacher didn't show up, so the students were left to themselves.
Tips
usage
Two registers: literal — to actually pasture sheep. Figurative — when supervisors abdicate, leaving people unsupervised. Common in classrooms (老师放羊 'the teacher let the class run wild'), workplaces, and parenting (放羊式管理 'hands-off management').
memory
Verb-object: 放 (to release / let out) + 羊 (sheep). Picture a shepherd opening the gate at dawn — same image as 'unleashing' a class of bored students.