Agreement Again! (One Child + Their = Error)

While checking out a new website on alternative health practices recently, I came across the following sentence:

What she realized was that even though the classroom can serve as a wonderful learning environment, the true source of a child's behavior and conditioning comes from their environment and mainly their home.

Oops! If you refer to one child, then you must use a singular pronoun (his or her) to refer back to that child. You may only use their if you are referring to children (plural).

Because you don't know or care whether this is a male or female child, the solution for this one becomes a little awkward. Do you really want to say "his or "her" twice in the same sentence, as in:

...the true source of a child's behavior and conditioning comes from his or her environment and mainly his or her home.

Probably not, but a closer look at this sentence brings up another point: The home is part of the environment, so eliminating the word "and" clarifies the meaning and also solves the wordiness problem.

I'm not comfortable saying that the source "comes from" something, so I would probably reword that part of the sentence as follows:

...the true source of a child's behavior and conditioning is his or her environment--mainly the home.

I'm also not overly fond of "his or her," and I'm not sure the designation is necessary here. In the end, I would probably rewrite the sentence this way:

What she realized was that even though the classroom can serve as a wonderful learning environment, the true source of a child's behavior and conditioning is the environment outside the classroom--mainly the home.

My guess is that this is probably what the writer meant to say in the first place.