The SCORM package itself controls when a new attempt is created - the package must set the cmi.core.lesson_status for the attempt to either 'completed' or 'passed' before a "new" attempt can be generated - if this is not set, then each time you enter the SCORM you will be working on the same "first" attempt, this is just how SCORM works. - more info on this here:
http://docs.moodle.org/19/en/SCORM_FAQ#Handling_of_Multiple_Attempts

Also make sure you understand the 2 grading options "attempts grading" and "grading method"

Grading method affects how a single attempt is graded - more info here:
http://docs.moodle.org/19/en/SCORM_FAQ#SCORM_and_the_Gradebook

Attempts Grading allows you to select how multiple "attempts" should be graded.

hope that helps!