I think most of us at one time or another feel the itch to go ahead and jump into Year 1, since after all our little ones can already handle the reading and many if not most of the other activities. Why wait? And we get lots of outside pressure, in many cases, to be doing formal school rather than this "whatever-it-is" that we call Year 0.
I don’t say this to imply that anyone is wrong for pressing on with Year 1 early, but just to let you know that there are good reasons for waiting. You may decide that despite those reasons it is worth starting in, and that’s ok.
Year 0 is a lot more than just read-alouds. (In fact, read-alouds are really a very small part of it. CM didn’t recommend spending huge amounts of time reading to the children in the early years anyway. She wanted them to be up and around.) There’s so much more to focus on, including habit training and nature study (and lots and lots of time spent outside just running around), and those things are *extremely important*, not just nice-to-haves or something to kill time before the kids are ready for "real school". If you start doing Year 1, you may find that you are keeping the kids inside much of the time to "do school" and robbing them of the outside time they need. There isn’t really a Year 0 booklist; those books are just some suggestions to get you started. The Year 0 Yahoo group has some booklists, or you could use FIAR as many do. But I’ve found that as we’ve emphasized outside time more (the goal is 4-6 hours *a day* remember!) we don’t need so many books to read because we’re not inside reading.
One of the benefits to waiting until age 6 (or thereabouts) to start Year 1 is having time to get the extras firmly entrenched in your family schedule before you have the pressure of school. For instance, this is a great time to start doing art study, composer study, poetry, tea time, physical education, foreign language, hymns, folk music, etc. If you get those subjects going smoothly, then you can add in the Year 1 subjects without so much stress. Habit training makes life easier for everyone, and this is a great time to work on it intensively. You can still teach many of the concepts you want to teach without making it school. Math is easily covered through games, cooking, and other real life situations. Pre-reading and even early reading lessons can be done very casually, but you could even do a formal reading program without having to start Year 1.
Starting Year 1 early may lead you to have to slow things down later, when the readings get much more intense. That’s another factor to consider. In a few years the readings take a big jump in difficulty and in the maturity of the themes, so you may find that you need to do one of those years for two years to give your kids time to mature before moving on.
CM very strongly encouraged parents to delay formal education until approximately age 6, for a whole host of reasons. Children need time to really play, to imagine, to run and jump and breathe fresh air, to explore the world around them without interference, to let their brains mature without a lot of strain. She’s not alone in recommending this, and research supports her. So I guess I am just suggesting that it might be worth looking at this time not as "wasted" but as valuable preparation for the later years, even if the preparation doesn’t look like school.