Students should play particular lines or measures that they cannot execute properly many more times than they should play the entire piece. Then they should go through the entire piece and play the difficult section in its musical context. Generally, when a student is beginning a new piece, the slower the practice, the faster learning takes place. Students should not attempt to play a new piece at a fast tempo. It all ends up being a waste of time.
Fast tempos come gradually after all the elements of a piece have been mastered.
Every student should have a metronome by the time he finishes level three. These expensive, but essential devices are the best way to start a piece very slowly and learn it gradually faster until the ultimate tempo has been achieved. Many students may find it useful to divide their practice time into two shorter sessions. Just be sure the total adds up to the goal of practice time established by your teacher for a student on your level. Organize a series of manageable goals that can be realized in the practice session.