Time to Stop

Today I started teaching E how to multiply and divide decimals.
I knew that he had a strong foundation with his multiplying and dividing so it shouldn't be a problem.

And he did great. Picked it up very quickly.

But there comes a time when a student has reached their limit for the day and I should have seen the signs.

He was looking at his fingernails .... getting up to play piano between questions ..... humming a song. But nooooooo, I wanted to do one more example.
And then this happened.

Me: So you've dealt with the decimals now just go ahead and divide. Sixteen divided into 2 is....?

E: 1.

Me: Well, no. Look at it. Sixteen things divided into 2 groups....you've done this a million times.....how many in each group?

E: 1.

Me: How are you figuring that? Look at this picture. See the groups? OO See the things? |||||||||||||||| Now divide them equally into the two groups.

E: There would be 8 in each group.

Me: Right. So 16/2=?

E: 1.

Me: Where are you even getting the 1 from? I see a 16, an 8 and a 2. Where is there a 1?

E: Well there's one sixteen.

Me: (Silence). Oh. Kay. Erase the 1.

E: Should I put an 8 there then?

Aa-a-a-a-a-and we're done math for the day.