Please change the command to something else. Submit is filled with many negative connotations and school is hard enough as it is. Kids don't need any more discouragement.

Suggestions:

• Turn In
• Completed
• Ready for Grading
• Done
• Complete
• Finished
• Here's My Work
• Please Accept
• Achieved
• Accomplished
• Concluded
• All Done
• Mischief Managed

Ok, maybe that last one isn't the best option, but you get where I'm going, right? 

Sincerely,

Susan