I've done a rough draft of the forms for my fiance's application and that form is for the sponsor. For myself I checked off university and put 5 years because that's how many years I attended university for. In the guide for question 5, form 5540 it says "Check the appropriate box to indicate your highest level of education and provide the number of years of study completed." I took that to mean the number of years of study at that level, so if highschool/secondary is from 9-12, I understand that u would write "4 years." But really it can be interpreted in different ways... that's how I interpreted it....
Perhaps some other people will chime in and explain how they interpreted it.... It could be total education (encompassing elementary and secondary) and in that case would be 12 years.... on mine though, I put the number of years at that particular level....
Sorry, not much help... you could try the call centre and ask them, however, I've heard that depending on who u talk to, different answers are often given...
Now looking at it, I'm second guessing myself and thinking that it should be that's the highest level completed and how many years in total for all education.... therefore in your case it would be 12.... BAH! I don't know. Sorry for rambling and not being helpful.... the more I look and analyze the more I second guess my initial reaction.