I asked:
> 10) Many children do seem to have a desire to do good. How
> can this be explained, if they do not yet have a Yetzer Tov?

Cantor Wolberg responded:
> 10) ... The child doesn't have a fully developed yetzer tov,
> but the potential and bud is there. 

I will now admit that my question was sort of rhetorical. I do not 
understand how it can be said that children do not have a yetzer tov. 
Cantor Wohlberg and I seem to agree that children do seem to have at 
least a partially-developed yetzer tov.

I also asked:
> 11) Has anyone noticed (either in themselves or in someone
> else) that this desire to do good either appears or gets
> stronger at bar/bas mitzvah age?

Cantor Wolberg responded:
> 11) Just as the desire to do good gets stronger at bar/bat
> mitzvah age, so too, does the desire to do bad also
> increases.  Hence, the battle is harder.

Again, we seem to agree that these aspects of a person develop over 
time. They seem no different than any other aspect of a person, such 
as physical strength, mental abilities, and all sorts of other things.

Someone else had asked:
> What happens at thirteen that makes the yetzer ha'tov come
> to life?  Is it biological? Is it related to sexual
> development? Is it social?

R' Akiva Atwood responded:
> ... Puberty -- and the social expectations on the "soon-to-be"
> husband/father -- force the person into a more responsible
> course of action. ...

>From his inclusion of the word "more", it seems that he too would 
agree that this sense of responsibility existed even as a child, but 
at puberty certain circumstances help the yetzer tov to mature and 
strengthen.

But wouldn't this also occur under other circumstances? For example, 
a child (of any age) who loses a parent will tend to find that he 
must suddenly mature in unexpected ways. There were many events 
scattered throughout both my childhood and adult life which made a 
profound impact on my personality, and I fail to see why this Medrash 
assigns particular significance to the age of bar/bas mitzvah.

Furthermore, however one would interpret this Medrash, we cannot deny 
that it puts a different timetable to the development of the yetzer 
tov than to the development of the yetzer hara. Why would this be? 
The sense of responsibility which RAA cited can be just as easily 
offset by the sense of independence which a young adult feels.

In summary, I would say that I find this Medrash (which RYGB 
summarized as "that while  one is born with his or her yetzer ho'ra, 
the yetzer ha'tov only begins its development at the age of bar or 
bas mitzvah") to be extremely difficult to understand. It seems to go 
against what we remember of our own childhoods, and what we see in 
others' childhoods.

And so I reiterate some of the questions that we posted in the OP of 
this thread:

1) What was the deeper basis for the assumption made in Koheles 
Rabbah?

2) Do Chazal address this issue in greater detail anywhere else?

4) Were Abraham's theological musings as a child as reported in the 
Midrashic literature detached from his moral development or did they 
occur after he was thirteen years old?

Or, in short, what does this Medrash MEAN???

Akiva Miller