Well, if the dancers are used to hearing AABB and then somebody demands an AB at the end, no wonder the dancers are getting confused.

Assuming that somebody else brings the music and you have no power over it, these tips might be helpful:

If the A part is major, then there's probably a couple measures of minor when the B part starts, or close to the start. Then the tune will return to major. Listen for that change.

Similarly, if the A part is minor, then there's probably a couple of major measures near the start of the B part.

An A part is usually more melodious than a B part. B parts tend to be more mechanical or march-like.

The highest notes are often in the first few measures of the B part.

These tips apply especially to so-called Celtic music.

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At my house, we have plenty of power over the music. I can take my MIDI files and my Noteworthy Composer program and have my way with any tune!

If a tune is nothing but eighth notes,(something that's all too common) I change the timing of some of them so that there are identifiable long notes somewhere. This is a help in finding one's place.

We have a tradition that when it's time to repeat, I play a trill on my recorder. It's just a way of letting one musician help another out.

If it's an early tune, the greatest way to let people know where we are is to put on a 'Picardie ending.' This is where a tune that been using Am chord (for example) suddenly uses an A chord, usually at the end of a phrase. Nobody can miss that.

When things are falling apart, somebody hollers 'top!', meaning go to the start of the piece. It's important to distinguish 'Top!' from 'Hup!', however.

Hope this helps a little.