If it is consensual, then no, I wouldn't report it to the state as abuse. If it were nonconsensual, then I would be required to report it as abuse anyhow.
Being a mandated reporter is very formalized. There's a set of forms and I have a 48 hour period in which to report things like suicide attempts, domestic violence and abuse. Interestingly, in cases where I am REQUIRED to report, I can't just report to people who actually could help. In fact, reporting is done by calling the CPS and the police.
Consensual sex between minors I woudn't report to the state (i.e., fill out paper work and call the cops). I would probably report them to the school psych or the social worker or the health worker and possibly their parents, which is NOT part of the mandated-reporter bit. But to the state as part of the abuse process, it would never occur to me to do so. And if every teacher did, the state would be fucked 2000 times over to deal with all the cases.
And, in the case where I suspected statutory rape 2 years ago (consensual sex between a minor and an 18 year old) I actually worked with the kid, as did the school psych and the health worker on campus. And I also eventually got her to break up with him. But I didn't report it and the school psych, who knows the ins and outs of reporting for mandated-reporter stuff, never mentioned that I should. So I guess statutory rape isn't mandated reporting.