上学(shàng xué) - to go to school, to attend school in Mandarin

上学 (shàng xué) is the daily routine of attending school, the exact counterpart of 上班 (shàng bān, to go to work). Both use 上 in its "turn up and do your session" sense.

It is a verb-object compound, which means the two halves can be split by anything that would normally follow a verb: 上过学 (has been to school), 上了三年学 (attended for three years). You cannot put an object after it, so "attend that school" is 在那所学校上学, never 上学那所学校.

For starting school for the first time, 上学 works, but 上小学 (start primary school) or 入学 (enrol) is more precise. Its opposite in the daily sense is 放学 (fàng xué, school finishes).