I am still learning this too.
First I thought I learned this semi correct thing, that
like is used to compare two things and
as is used to compare two actions.
Maybe that is not exactly right, but it gets one started in the right direction.
For instance, you might say,
Jim's dog is like Ken's. They both have long fur.
I guess it's pretty clear you would not say
Jim's dog is as Ken's.
So in this comparison of two things,
like is definitely the way to go.
So what is
as used for?
Well one thing I read, I did an online search, is that
as is used similarly to how one uses
the way.
So in your sample sentence one could put it
Law students learn to think the way a lawyer does.
It's not comparing anything really now that I consider it. It's saying that they learn to think the way a lawyer does.
So we say
Law students learn to think as a lawyer does.
So in that case, using
as is sure thing.
Here's another one.
Jim runs like Henry. We wouldn't say
Jim runs the way Henry. So
like is good here, for sure.
We would say
Jim runs the way Henry does. So we would also say
Jim runs as Henry does.
One good explanation for all this is that
like is used similarly to how a preposition is used and
as is more of a conjunction.
So
as connects two subject verb clauses. For instance in
He fights as a wildcat fights. the
as connects
He fights and
a wildcat fights.
In your original example
as connects
Law students learn to
lawyer does.
If you ask me, it's all a little weird, and the reasoning behind the choices is not that clear. For instance, does it really make sense to say
Jim runs like Henry? It sounds to me as if one is comparing
runs to
Henry. So while
Jim runs like Henry is supposedly acceptable I personally don't like it that much, and maybe on the GMAT you have a choice between
Jim runs like Henry and
Jim runs as Henry does the latter would be the credited answer. That just a guess though. I could be wrong on that.
Still, I pretty much get it at this point, and maybe now you do to.
For more on this there is a good explanation with a quick reference list here,
https://alt-usage-english.org/excerpts/fxlikevs.html, and I am sure by doing a search on these forums you can find even more.
