Empty 'Data'

Hi
I Have the following code as part of my Before Record Added event:
*// Parameters:

// $values - Array object.

// Each field on the Add form is represented as a 'Field name'-'Field value' pair
// If action is Think Tank

//** Insert a record into another table ****

if ($values["SuggestedAction"]=6)

{

global $conn;
$str = "INSERT INTO thinktank (StudentId, ReferDate) values (";
$str .= $values["StudentId"];

$str .= ",";

$str .= $values["IncidentDateAndTime"];

$str .= ")";
// echo $str;

// return true;
db_exec($str,$conn);
}
*
When it is executed it produces the following output:
INSERT INTO thinktank (StudentId, ReferDate) values (,)
I know I must be doing something wrong that is simple, but can't work it out.