Originally Posted by
Super27
This is the route I would pursue. Except it doesn't have to be the "highest" level of privileges. You can take the check for any ONE of the ratings that's on your expired certificate, and ALL will be reinstated (14 CFR 61.199(a)(1)). When I let mine lapse a number of years ago, I elected to take just the CFI-A check, and my CFI-I and MEI were also reinstated.
This is correct you don't need to takje them all, or even the "highest" instructor rating (whatever that is). You can take the checkride for any CFI rating you held, and that will re-instate them all. CFI-I or MEI would probably be easiest.
Although if you're planing on teaching someone to fly, the CFI-A would probably be most useful to you, although that's a more involved ride.