When you’re marking an exercise for a pianist, speak in terms of counts rather than bars, particularly with introductions (e.g. say ‘x counts in’, rather than ‘x bars in’).
Unless you are trying to work out the mathematical correspondences between a movement notation score and printed music, bars are confusing, and often irrelevant, both to teachers and pianists. Some novice pianists might ask you ‘how many bars do you mean’ if you talk in counts, but don’t get drawn into this beyond a discussion of general principles, otherwise you’ll spend half the class going over to the piano trying to sort out the pianist’s sheet music!
It’s for the pianist to get used to the idea of feeling the counts underlying the notation if they’re using printed music. Contrary to what you’ll hear dancers say against themselves, this isn’t some philosophical divide between musicians and dancers: Musicians who don’t conventionally work from notation (like rock bands – think of the drumstick ‘count-in’, for example) have no problem understanding the concept of counts.