Just Say No...to one-year old...

[DaycareLady]

My daughter is 14 months and she absolutely understands "no", "don't touch", "out of your mouth" etc. But she will look right at me with a smirk and do it anyways! In that case I remove her and redirect her to a different toy/area (and she throws a huge fit but doesn't go back to whatever it was she was doing that I asked her not to). They love to test their limits at this age and see what they can get away with! I say, just be consistent!
I also have a 12 month old and a 13 month in care and they both look at me if I say "no" and usually listen!

[Sassygirl]

Try saying "Stop" instead? I currently have 3 full time 11-14 month olds plus my own 12 month old and they ALL know what "No" means and all smile and continue doing what they aren't supposed to be doing.
I have tried saying "Stop" and getting down to their level, stern voice, eye contact. Sometimes works, sometimes doesn't. In my experience though, I find when they are tired they are even MORE defiant.
I have my daycare on the main floor of my house so our playroom is gated off and I have a "confinement" playpen in the dining room in plain site. If after 3 strikes kiddos go in there for a few minutes then are welcome to return back to our group. Doesn't take long but they "get it".