Another very common change in "context" that is oftentimes overlooked is the onset of new motor skills, most notably rolling over, crawling, and walking. All these fabulous physical milestones change the way your baby sees the world in fundamental ways. Here's one of many similar questions I've received:

I just received your book and found out that we are now entering a good
sleep training phase since my son turns 1 this coming Friday.  I want to get
him to start falling asleep on his own, but if I try to put him in his crib
while he's only half asleep, he just stands right up like he's on automatic
pilot.  If I then leave him he starts to cry and I don't want to use any of
the CIO methods. Besides, that doesn't work with him because it just
escalates into a frenzy. I still have his crib in our room and want to get
him into a firm sleep habit before trying to move him into his own room. I
can't figure out how to get him to relax though….

This is a classic age when SOME kids have a hard time falling asleep. And it has a lot to do with the new motor skills they're learning and practicing — namely walking. About the 12th month mark is when many kids start learning to walk and all hell can break loose with their sleep habits because their little minds and bodies are furiously practicing. By the way, children can start walking as early as 8 months (oh… I pity the parents that have to deal with those little daredevils) and as late as 18 months with no long-term benefits or problems. When we watch people do things, even if we are currently not doing them ourselves, a fascinating thing happens in our brains. The same pattern of neurons fire whether we're watching someone move their arm , for example, or if we ourselves are moving that arm. This  fascinating discovery is considered by some to be the most important one made by neoroscientists for decades –  "mirror neurons." So it may be that when children are watching others walking and when they are put in their cribs alone, what they are doing is not only moving their feet, poppinp up and down holding the bars of the cribs, cycling their little legs, and so on. They are also probably imagining the act of walking — both when they're awake and asleep, dreaming. This may be why many kids' sleep is disrupted as they're at the cusp of mastering physical skills. There are no direct studies that have mapped the neuronal activities of babies asleep in their cribs when they're just starting to walk, but that would be my strong hunch of what's going on.

The same holds true of the other major physical milestones — they too have the potential to disrupt sleep. So, rolling over (around 5-6 months), crawling (around 8-10 months) and walking (around 12-14 months) may be difficult times for sleep training also (Again, please keep in mind that these age-spans are approximate. My kids didn't hit any of these milestones "on time" if that matters to anyone). And remember the title of this post was supposed to be the continuation of Part I and Part II about how context can have an impact on sleep-training or can disrupt already well-established sleep habits. The reason this post is also about context is that when children learn new motor skills their WHOLE WORLD is blown apart. So many of the most important parts of their contexts undergo radical changes. The baby that can suddenly roll over begins to feel the wonder of intentionally changing their body posture, their view, their physical feeling of how the exist in the world. The baby who can finally crawl finally feels the incredible miracle of being able to reach and chase stuff that's so far been out of his reach. The baby who previously had to point or squak to get you to get her some toy across the room can now DO IT HERSELF!  YIPPEEEEE! Now mulitply that miracle by 100 when walking begins. Oh how fast he can now move to the desired object! How much fun it is to hurl yourself onto couches and into grass and to push, push, push chairs and tables and plastic lawn mowers and so, so much more. The world around these babies is indeed changing dramatically and, as we talked about before, these shifts in contexts can have a major impact on sleep (as well as moods and thinking styles… but that's another post).