"You speak with the teacher sometimes."
Translation:Tú hablas con la maestra a veces.
Wait a minute, don't you have to say 'you sometimes speak with the teacher'. The adverbs of frequencly have to come between the subject and the thing that the subject never/always/often/frequrntly/ever/etc. do. I am not a native english speaker and have english on school, my english teacher talks a whole lesdon about this rule, and than Duolingo comes and broke it!
I remember studying the theory of syntax and asking my professor why we never talked about adverbs. His reply was something along the lines of "I guess because there's no need. They can go anywhere."
Real life says otherwise. Probably that whole theory versus practice thing.
I now believe that, like other words, each adverb comes with its own set of rules and tendencies, but that the rules for similar words are often similar.
Most of the adverbs you list (never/always/often/frequently) are "adverbs of indefinite frequency".
As said in
"Adverbs of indefinite frequency mainly go in MID position in the sentence. They go before the main verb (except the main verb 'to be')[.]"
But, that same web page also says
"Occasionally, sometimes, often, frequently and usually can also go at the beginning or end of a sentence:"
Also, on that web page is a discussion of adverbs of definite frequency.
You also list the adverb "ever". That carries its own complications, described at