Highly vs. high

I understand that, in the following phrase and sentence the adverb 'highly' is used to mean 'very'. Now I am just wondering if the word 'high' could be also used instead of 'highly' . To me, substituting 'highly' for 'high' in the following examples sounds very awkward. But, according to a dictionary, 'high' is used as an adverb and it could mean not only ' far from bottom/ground' but also 'high in amount or value' depending on the context.


highly educated students
It is highly unlikely that she'll be late