Studies have shown that students learn much faster when their attention is directed to the subject at hand. If they are on their phones, or reading something else, or writing notes to a neighbor, they might be listening, but they aren’t retaining much at all.
If their attention is directed to the topic, such as with questions asked ahead of time, then the students are generally much more engaged. Their scores go up. They learn more, and they retain more of what they learned.
Therefore, it is very important to ask questions first, then sing the song so they know what they are listening for, then take responses. Keep repeating.
When learning a song, try to aim for 8-10 repetitions of the students hearing the song, interspersed with short singing experiences, before they attempt to sing all of it with you. You will likely be pleasantly surprised at the results!
However, if they don’t know what they are listening for, or if they are engaged in other activities, they might not retain as much information at first. So keep their attention on the song, including the words, the melody, the rhythm, and they actions if they are used, and see what happens!