Can my grown son claim me as a dependent when I was taking care of my grandkids in exc. for rm and board and I did work part of the yr and claimed myself as a deduction?

No ... if you made more than $4200 you cannot be a dependent ... you will file your own return.

I earned less (and claimed myself as a deduction on w4) but our (business?) Agreement was i was keeping kids ect in exchange for room and board. No agreement he would claim me! Now I lost stimulus.

@laorlik - he can only claim you If

• he is providing more than 50% of your financial support (room and board, clothing, transportation, utilities, medical expenses, insurance, etc.)
• you make less than $4200 per year (excluding social security)
• you are a U.S. resident alien, U.S. national, or a resident of Canada or Mexico.

the way it works is...

from his perspective,  he has the option of claiming you if all 3 items above are true; however, the IRS does not require it (if any one of the 3 items are false, he can not claim you)

from your standpoint, if he CAN claim you whether he does or not, you are not eligible for the stimulus

so he has an option, but you are 'stuck' regardless of what he does. 

here are the eligibility rules for stimulus: 

A1.  You may be eligible to receive a Payment if you:

• Are a U.S. citizen or U.S. resident alien;

• Cannot

  be claimed as a dependent on someone else’s return;
• Have a Social Security number (SSN) that is valid for employment (valid SSN); and
• Exception: If either spouse is a member of the U.S. Armed Forces at any time during the taxable year, then only one spouse needs to have a valid SSN
• Have adjusted gross income below an amount based on your filing status and the number of your qualifying children.

Thanks so much! Under your "rules" he didn't provide more than 50% of my needs for the year. I did attempt to file and my return was rejected. So now after already having a war over this, I have to file by mail if I want to submit my appeal ..

Correct ... mailing is your only option.

What happens to him (his return) if I do so? Does he lose his refund? What if he already received it and disputes my dispute?!

He must also amend his return ... but you can file now and he can do it later ... and of course he will lose all the benefits he got from claiming you and will have to pay it back.   So ... if you are only doing this to get the stimulus check now then you can let sleeping dogs lie and on the 2020 return you can claim yourself and get the stimulus credit next year.