Correct punctuation for he said, she said

Question

It was recently suggested to me that when attributing dialogue after a quote it should always end comma close quote lowercase, as in:

"That's what," he said.

However, if the character speaks in complete sentences is it ever correct to end full stop close quote?

"...with a pound of grapes and nothing more." She said.

It would seem correct to capitalise after a question such as

"Where do you think you are going?" Said Mother.

Is there an accepted convention here that I am unaware of or is the second example always wrong/right?

Answer 1

No, the complete sentence includes the quote and the attribution:

"That's what," he said.

"...with a pound of grapes and nothing more," she said.

"Where do you think you're going?" said Mother.

Answer 2

You may end a quote with a question mark or exclamation point (and of course a comma) without completing a sentence. A grammar textbook or style manual will benefit your ongoing pursuits. THE CHICAGO MANUAL OF STYLE is a widely accepted resource and is what I use. You may end a quote with a period, but then you need a new idea to follow. You may also split a quote:

"Let's see," Bob began, "you took the dog to the park before going to the store?" He didn't wait for a response before saying, "I can't believe you did that."