EarMaster. Far and away my top recommendation. I use it school-wide, for K-8 and adults. It is cheap ($4 a month) and worth $100 a month. Take a beginner singer, and put them through built-in the starter course, with your guidance.

SingTrue is useful. However, you'll spend a few bucks on that too. You can spend $4 for a very, very limited solution (SingTrue) or a $4 a month for a few months on a hugely powerful, total solution in EarMaster.

@davido I disagree with your assessment. I did my Master's thesis on the subject, and there are many, many individualized factors beyond vocal technique, a substantial number which can be addressed via a program EarMaster. (There are other programs, like through MusicFirst, which offer similar, though less substantial, solutions.) Of course vocal technique is a huge part of the pie chart, but it's not the whole pie.

I use and have used a free guitar tuning app to fix some of my own pitch issues. Some people have no idea they are sharp or flat, they just sing as if everything is just fine. Some people have issues with hearing the pitch and recognizing that that the pitch they are singing does not match the one they are singing. So they have learned the pitch wrong for their whole lives.

If your student(s) down loads the app, plays a pitch on the piano or other app or instrument, sings that note, then checks it against the tuner, they will see that they are sharp or flat and can adjust accordingly.

Only by knowing where you are can you know how to fix it. Once they begin to learn what the note should actually sound like, will they be able to sing it properly.

IMHO.

I have suggested this to some members in my choir and I can tell who is doing it and who is not.

i tried out a tuning app recently and was SHOCKED (but not that much) about how out of tune I sing and a lot of things in my life became a lot clearer

Do you believe . . . in Auto-Tune?

That's a good idea. The apps can be good for general pitch comparison and the like, but not very good for matching pitch while singing. I think I will try a chromatic tuner with my voice students and see if the visual feed back helps.

Does anyone find that singers who also have a musical instrument background have as many problems with intonation?

When it comes to singing, we may very well have the correct pitch in our mind, but due to faulty singing technique the pitch we produce may not match the pitch we intend. The fundamental pitch is determined my the vibration of the vocal folds, but our vocal tract has a major influence on the overall vocal sound that others hear. If the vocal tract is not shaped correctly to tune the overtones the pitch will be perceived as flat/sharp etc. This is often due to excess tension in muscles that should not be tense, or perhaps not enough muscle tension. While other wind instruments are more rigid/fixed, the human voice is in a constant state of flux and needs to be constantly tuned/fine tuned throughout the singing process. Also, the fact that we perceive our own voices differently than how others perceive our voices is a major hurdle to overcome. Much of voice training is overcoming habitual use of the voice.

While singing training either through private lessons or through a good choral program will improve singing technique, listening exercises are still required to train the inner ear and mind to perceive the pitch. How can a singer sing a particular interval unless there is a concept of that interval in the mind? And singing alone is different than singing with an ensemble where the singers have to tune to each other.

I find the students I work with (mostly seminarians) struggle in both areas. When I was teaching mostly high school aged voice students I focused on singing technique almost exclusively. They already had the music in their ear and needed help refining their voices to audition for the H.S. musical and the like. Now, in addition to that, I find many don't even have a concept of a scale, whole or half step (not to mention rhythm) and so much remedial work is needed. I don't get enough time with them to correct all the faults, but basic ear training and musicianship should have been learned at a much earlier age. That doesn't seem to be happening today. I suppose most people are growing up with bad musical/vocal models or no music at all.