user21457: So, in a tournament, my daughter recently had a case where her opponent made a move and declared checkmate. She acquiesced, shook his hand, and then realized it wasn't actually a checkmate. They continued the game until she actually checkmated him, at which point he said, "Well, you shook hands.." and claimed the victory in the tournament.
I can see both sides of this, but I am really not sure what the official ruling in a case like this would be. Anyone have any thoughts?

user20721: It all depends.
What tournament where when?
Who ran it?
What rules were being used.
FIDE would require signing the score sheet.
Shaking hands means nothing except you like spreading germs around.
If he kept playing on after she did that would pretty much prove it was not mate and overrule any claims that she resigned. 
Your kid should refer to
""<<
21F3. Facts are not agreed upon.
If the facts are not agreed upon, the director should proceed as follows:a. A director who is satisfied that the facts have been ascertained should rule accordingly.
b. A director who is unable to satisfactorily determine the facts must make a ruling that will permit play to continue.
See also 1C2, Director discretion; 
"">>""
say the facts are not agreed on.  Use the position on the board as proof.  and ask also for a ruling on the facts and also if needed IC2  Director discretion.
Especially since this is a kiddie tournament the TD should not award the win even if there was a meaningless handshake to the person who made an erroneous claim. 
Depending on other factors they might caution the claimant against making claims so as to win improperly and to let the other person realize that it is actually or else  move as in this case when it was not mate. 
Situations like this emphasize the need to know ALL the rules if one is going to play in a tournament. Some groups may modify the rules or elaborate on them. 
Start here:https://new.uschess.org/wp-content/uploads/2018/12/US-Chess-Rule-Book-Online-Only-Edition-Chapters-1-2-11-1-1-20-1.pdf

user8201: Checkmate ends the game - there is no agreement/concession involved. If it’s not checkmate the game has not ended. And a handshake is not a move which needs to be “retracted”.
If the error was only realised significantly later, then maybe it’s a different case. I can see that an arbiter might deem the handshake to be a resignation. But that’s not the case here: they just played on and did not mark the scoresheets.
Your daughter does not need to be an expert in the rules (which cannot not be exhaustive in any case) but does need the reflex to call the arbiter or tournament director in any kind of dodgy situation.

21457: <p>So, in a tournament, my daughter recently had a case where her opponent made a move and declared checkmate. She acquiesced, shook his hand, and then realized it wasn't actually a checkmate. They continued the game until she actually checkmated him, at which point he said, "Well, you shook hands.." and claimed the victory in the tournament.</p>

<p>I can see both sides of this, but I am really not sure what the official ruling in a case like this would be. Anyone have any thoughts?</p>
 20721: <p>It all depends.</p>

<p>What tournament where when?
Who ran it?
What rules were being used.</p>

<p>FIDE would require signing the score sheet.</p>

<p>Shaking hands means nothing except you like spreading germs around.</p>

<p>If he kept playing on after she did that would pretty much prove it was not mate and overrule any claims that she resigned. </p>

<p>Your kid should refer to
""&lt;&lt;
21F3. Facts are not agreed upon.
If the facts are not agreed upon, the director should proceed as follows:a. A director who is satisfied that the facts have been ascertained should rule accordingly.
b. A director who is unable to satisfactorily determine the facts must make a ruling that will permit play to continue.
See also 1C2, Director discretion; 
"">>""</p>

<p>say the facts are not agreed on.  Use the position on the board as proof.  and ask also for a ruling on the facts and also if needed IC2  Director discretion.</p>

<p>Especially since this is a kiddie tournament the TD should not award the win even if there was a meaningless handshake to the person who made an erroneous claim. </p>

<p>Depending on other factors they might caution the claimant against making claims so as to win improperly and to let the other person realize that it is actually or else  move as in this case when it was not mate. </p>

<p>Situations like this emphasize the need to know ALL the rules if one is going to play in a tournament. Some groups may modify the rules or elaborate on them. </p>

<p>Start here:<a href="https://new.uschess.org/wp-content/uploads/2018/12/US-Chess-Rule-Book-Online-Only-Edition-Chapters-1-2-11-1-1-20-1.pdf" rel="nofollow noreferrer">https://new.uschess.org/wp-content/uploads/2018/12/US-Chess-Rule-Book-Online-Only-Edition-Chapters-1-2-11-1-1-20-1.pdf</a></p>
 8201: <p>Checkmate ends the game - there is no agreement/concession involved. If it’s not checkmate the game has not ended. And a handshake is not a move which needs to be “retracted”.</p>

<p>If the error was only realised significantly later, then maybe it’s a different case. I can see that an arbiter might deem the handshake to be a resignation. But that’s not the case here: they just played on and did not mark the scoresheets.</p>

<p>Your daughter does not need to be an expert in the rules (which cannot not be exhaustive in any case) but does need the reflex to call the arbiter or tournament director in any kind of dodgy situation.</p>
