The real answer is never, but if you press on for an answer, it’s as soon as your baby can repeat words back to you in an instant. You might think that as soon as you baby first becomes verbal that signing becomes obsolete, but this isn’t so. Up until your baby is into his verbal explosion where he’s adding multiple words a day, signing will still play a part in your baby’s life.
As my son neared two, he began to replace many of his signed words with spoken words. In fact, his signed words were usually the ones he’d speak first over other words, but occasionally he would surprise us with fresh spoken words. His signs helped him encode the spoken words because he already understood their use all he had to do was wait until his vocal cords caught up to his desire to use them.
A signing child will always use his signing background in language. This isn’t a direct reference to using signs along with speech or using signs as replacement to speech, but rather a reference to using the framework and experience of signs in his communication development. Just as a toddler will use play into his adult years, and not for play, but for skills related to life in general, a signing baby will use his signing skills in communication. All things we do set us up for things later in life. Take music by example. It’s been said many times that music helps in mathematics because the mental processing is similar. One might also look at team sports such as soccer or hockey and see that this sets up cooperation and strategy. Individual sports like dance and gymnastics help in coordination and helps build confidence. Over and over again, science tells us that active body produce active minds with the more stimulation a person gets, the more dynamic they can be when novel tasks arise.
So while many parents rest on the theory that signing is temporary, I say it’s not even close. Signing is something that is going to stay in your child’s brain as a positive learning experience to be drawn on for his entire life. Baby signing is wiring his brain for communication from a very early age and as no one would deny, communication is vital to getting along in life.