While maintaining that same beat, try counting internally instead. For many novice pianists, the second attempt tends to fall apart at a faster rate. While the fingers continue to tap, the beat itself grows less certain. While internally counting may feel easier, because no one else hears it, it sometimes obscures exactly where rhythm begins to waver.
Counting externally gives rhythm a form outside your head. Quarter notes, half notes, eighth notes, and rests cease to merely be figures that you read on the page; they become something you can vocalize, clap, and check. When your voice clearly vocalizes the count, your fingers or instrument gain a firmer anchor. If your voice stumbles, drags out a number, or skips past a rest, you have pinpointed something worth addressing before you lose your way during a phrase.
Here is a powerful way to apply this strategy: eliminate pitch. Select two bars from an elementary piano piece. Ignore the note names. Clap the rhythm while simultaneously counting aloud at a slow tempo. Ensure longer notes are given their proper duration, and be sure to count rests rather than ignore them as non-events. A rest is still beat. Vocalizing the count over a rest trains you not to anticipate the next beat simply because you have no new note to play.
This skill is especially important when the eyes get involved. While searching for the next note on the page, a student might lose the beat. Rhythm is not always the issue; sometimes we are overtaxing our brain by trying to perform multiple tasks. Counting aloud separates the steady pulse from searching for the pitch. After the rhythm is somewhat secure, return to the staff. Read through the note names slowly. Then try putting the rhythm and note names together, but without the same level of stress. A metronome is helpful, but it should not take the place of your own count.
You need your own voice to count; use the metronome as a background resource rather than the primary instructor. Select a slightly slower-than-necessary tempo for your piece. Clap a short section, and count along with the clicks. If you cannot clearly vocalize the numbers, the pace is probably too rapid. Do not view slowing down as a step backward; it is merely providing the beat with ample room to stabilize.
Some musicians may avoid counting aloud because it feels awkward. If practicing in the presence of others, a whisper might not feel so strange; just softly speak your counts. You can also tap your beat with one hand, and count quietly with the other. Regardless, it is still critical that you can hear the rhythm to some extent, as otherwise it is easy to miss a subtle timing issue. Counting internally is fine once you have a clear understanding of how your body will keep the count.
You will notice counting aloud is helping your rhythm improve when you gain more ease in noticing rests. For example, you might go from thinking that an entire passage sounded bad, and then pinpointing that beat 3 came slightly early, that a half note was rushed, or that there was a rest somewhere in the middle. This level of insight will make your practice more manageable. Instead of repeating a difficult phrase five times from the start, drop the pitch and count the rhythm out loud; you will notice where the rhythm needs repair.