The correct usage of "too" and "also"

I always have problems in deciding whether to use "too" or "also". For example, if the previous sentence is:

Peter ate the cake.

Which of the following should I say?:

• He ate the pie too.
• He also ate the pie.

And what about?:

• He drank the juice too.
• He also drank the juice.

Another scenario:

Jack forgot his homework.

Which is the correct way to say "me too"?:

• I forgot my homework too.
• I, too, forgot my homework.
• (I have a feeling that "I also forgot my homework." is simply wrong in this case)

I guess I can sum up my question as follows:

1. If two sentences share the same subject, should I add "too" after the predicate or add "also" after the subject of the second sentence?
2. If two sentences share the same predicate, should I add "too" after the predicate or after the subject (with the commas)?

Solution 1:

I don't think they are interchangeable in every case. "I forgot my homework too" implies that you have forgotten your homework and some other thing(s), whereas, "I too forgot my homework" implies that you and someone else have forgotten to bring their homework. "Peter ate the pie too" or "Peter drank the juice too" means he ate/drank pie/juice and some other thing(s), and "Peter also ate the pie" or "Peter also drank the juice" means he and someone else ate/drank the pie/juice.

Solution 2:

"Too" and "also" both mean "in addition" and are interchangeable in all the examples you have given (even "I also forgot my homework").

1. You can use either.
2. Again you can use either, although the excessive use of commas (as in "I, too, forgot my homework" disjoints a sentence and makes it less readable).

edit: Online dictionaries corroborate these definitions (too, also) and whilst meaning can differ slightly or be ambiguous without context, they are used interchangeably in spoken English.