Underachievement is the fact or situation of people doing less well than they are able to. It is the noun of underachieve, and it belongs to reports, research, and policy debates rather than to conversation — you meet it in newspaper articles about schools, in government papers, and in the language of head teachers. It very often describes a pattern across a whole group over time, so it takes phrases like 'underachievement among boys', 'persistent underachievement', 'tackle underachievement'. It is uncountable: you talk about underachievement, not an underachievement. Because it names a gap between ability and result, it usually comes with a question about why — poor teaching, poverty, boredom, low expectations — which is why the word so often appears next to causes.

低成就表現（沒有發揮應有實力的現象，常用於教育議題）