[emartinelli]

I remember when I was studying English in the U.S. with other foreign students some years ago, when the topic was phrasal verbs the grades decreased for entire class. I am Brazilian, the class was composed most of South Koreans and Saudi Arabians.

[schoen]

Phrasal verbs are a hidden problem for estimating English vocabulary competence (as was alluded to earlier in this thread), because they play serious havoc with the idea of "knowing" a word. If you asked English learners if they knew the meanings of "work", "in", "out", and "off", most would say yes at a pretty early stage of their English education.

But that doesn't mean that they'd necessarily correctly interpret (or produce) "work in" 'incorporate (in a narrative or plan), "work out" 'resolve (a problem); deduce (a solution or consequence); deliberately perform physical exercise', "work off" 'eliminate (a debt, obligation, or excessive food intake) through effort'.

And there are hundreds more of those combinations with meanings that need to be learned independently.