Meaning trap
act up
misbehave
to behave badly or not follow the rules, especially for children or pets.
Don't mix these meanings
Same phrase, different job.
to behave badly or not follow the rules, especially for children or pets.
Another meaning of 'act up' is 'not work properly'; compare the examples to keep the meanings separate.
Hear it in context
Notice where the phrase sounds natural.
The kids started to act up as soon as the teacher left the room.
When my little brother acts up in public, my parents usually try to calm him down quickly.
Fix the pattern
One small grammar move makes it sound right.
Not: The kids are acting out again.
Say: The kids are acting up again.
For kids or pets misbehaving, use 'act up' (BrE 'play up'); 'act out' means expressing feelings through bad behaviour.
Which sounds natural?
Tap the one a native speaker would say.
'Act up' is the natural casual verb for kids misbehaving; the formal paraphrase sounds like a report.
Build natural chunks
Words that usually travel with it.
act up (misbehave)
- the kids
- started
- again
- be
Don't confuse it
Related
Other meanings and phrases to compare.
- act up (not work properly) — Another meaning of 'act up' is 'not work properly'; compare the examples to keep the meanings separate.