We had this problem at one point unfortunatly we now have a script to create users directly for our database. This might work:
In LDAP settings don't assign an e-mail field but set it to be locked.
Does your OU not hold e-mail addresses?
Sorry not to be more help.
What's stopping you from using a dummy email address for your year 7 students?
Nothing really but i would rather have it blank before i do that.
Ok thanks allot
To clarify what I was trying to say (admittedly a long shot).
Navigate to your LDAP authentication plug settings page in moodle "Settings link in Administration > Users > Authentication"
Scroll down until you get to Email: then set Lock value to be "Locked" (See screenshot).
It is possible, I tried this today at work.
Read this post on the moodle.org webstie and edit the relevant PHP files, you can choose whether e-mail is mandatory or not, and it does work!!