How do I disable the Notes App on ipads?
You cannot disable the Notes app in iOS devices, either with Restrictions or with Apple Configurator. There is no way I know of to delete or hide any of the pre-installed Apple apps, either.

You can lock each iPad to a single app using guided access, described here.

Your best mechanism for preventing this behavior is through social engineering: a clearly written Acceptable Use Policy signed off by by parent &amp; student; and trips to the principal's office, with penalties for infractions.