Electronic tuners are invaluable to beginning students.
It is difficult to know what an 'in tune' instrument sounds like if you only get your guitar tuned once a week at your lesson. For example, the low E string is normally tuned to E. However, tuning it down one step, and open E string will not play a Eb. This goes for the other strings as well. The best way of doing this is with an electronic tuner, and fretting the string on the first fret. The rest of the string remain to the same normal tuning.