I heard from a client I regularly arrange for that they were struggling with some syncopations – specifically, eighth-note anticipations of the downbeat.
In reflecting on how I teach in such situations, I discovered that the most frequent rhythmic noise I make in rehearsal is to strengthen this type of syncopation. Long after I stop audibly giving them the beat, I am snapping or clapping on the strong beat immediately preceding the syncopation.
I told my client to start by snapping both beat 4 and 4-and (where they sing). Then, take away the upbeat, leaving just a snap occurring on the eighth-note before they sing. When they are solid, you can also eliminate that sound, trusting that the singers will have ingrained the cue beat.
Teaching singers to hear a syncopation as a reaction to an immediately preceding beat is the most effective way I’ve found for consistency in these tricky rhythms.