If you started teaching signs at around 6 months...

[GuavaGirl]

...how long did it take for them to start signing back?

[Comtessa]

FOREVER!

DD and I started a sign-language class at around 10 months, but I was already teaching her a bunch of signs before then, starting at 6 months. I think her first sign was "light," and she started doing it around 10 months, right when we started the class. Each new sign takes a while before she starts to do it, and then she frequently drops a sign when she picks up a new one. For example, she almost never signs "book" anymore, though for a while it was her favorite sign.

It really, really depends on the baby. Some will pick up tons of signs, some never will. DD can do about a dozen signs at 15 months, but usually only uses 2 or 3 a day, even though I sign to her all day long. She understands some signs that she doesn't use, too. I suppose that's normal. Just keep on doing it and don't wait for him to sign back -- one day he'll just surprise you with it.

ETA: Signing has been a Really Really Good Thing in our household! So don't give up even if your LO takes forever to learn to sign! It cuts down SO much on DD's frustration. And in the case of the "milk" sign, it also prevents her tearing at my clothing, though she still does this if I don't stop immediately and nurse her the moment she makes the sign.

She has also started signing in her sleep. So cute.

[urchin_grey]

He started signing at 9m, but he wasn't consistent with it until around 13m. By 16m, he was picking up signs after seeing them once or twice.

[Abraisme]

I started signing with my DS at 7mo and he didn't sign back until 14mo. His language was always a bit delayed and he didn't start talking until 2yo.

I started with my DD around 7mo and she signed "milk" back at 10mo.

[kayabrink]

My babies seem to sign back quickly- about two weeks after I started, with ds, but he was older than 6 months! DD, I started at four months and she was using the sign 'milk' at 7 months, but she wasn't using it accurately- she often used it to nurse, but also occasionally to indicate that she wanted a random object- she would then sign 'milk' in the direction of said object. However, she is not at all consistent, she knows about 8 signs but will briefly stop using some of them. I can't figure it out. The only signs she does consistently are 'light' and 'music'- neither of which is really very important (in my opinion, obviously)
Anyways I'm on a rant now but suffice it to say it's a long and painful process.
Also, having started earlier with dd, I find she "babbles" with her hands more than ds- making random gestures that may or may not be signs, which makes it hard to distinguish actual signs.

[kismetbaby]

At about 9m. He's 10.5 months now and signs: dog, book, water, hat, ball, and waves bye-bye. He doesn't have any spoken words yet, so I'm glad that I have been doing sign with him. Even though he still seems pretty limited with the signs, its nice to see him have this way of expressing himself.

With all of his signs, it took me a couple days or even weeks to realize that what he was doing was a sign. So he may have been signing earlier, but I didn't catch it b/c his signs are kinda like baby-talk. . .they resemble the sign, but are some variation of it, especially at first. For ex: He just started signing water recently, but its with only one finger up by his mouth instead of three fingers.