Are you cooking from frozen? If so thaw them first.
Have you ever done this sort of thing before? Is that 1 hour you have for cook time or is that 1 hour for cook and serve?
This is only a guess because I don't know what your set up is there. I would say you should allow 15 to 30 minutes for service. Even if you have preplated self service, 140 kids will take a good 20 min to get their food and get seated. Plus your slicing and plating time...Say you get 10 serves each, that's 14 @ say 3 minutes to slice and plate each = 40 minutes!
The only thing I can suggest would be to change to somthing else. Something that can be cooked quicker and served easier and quicker. Cornish pastie come to mind. Or maybe sandwich platters...There's a go...sandwich platters. You can prep the day before (if needed) assemble the sangas on the day. For service you just need a table or two. The kids can stand to eat.
If you really want or must stay with the lasagna, then I can only suggest that you need to work out the logistics...not just the cooking time.
I hope that is of help