The NPRM is pretty vague; it's not clear at all. By "fabricating and assembling," does that mean I need to be winding my own motors? Does my foam airframe count as 10 pieces, or one? It's really not clear. Either way, as the NPRM is written, the excepted amateur built UAS would be still be restricted to FAA recognized identification area (FRIA) which (as proposed) could only be formed under the wings of a community based organization (as of yet undefined, none exist atm) within the first 12 months after the law went into effect. FRIA's would then phase out so within 3 years ALL sUAS would need to be RID compliant. Obviously this is ridiculous as it would outlaw any sort of homebuilt aircraft or multirotor, because the RID must be built into the aircraft and not be bypassable by the operator.
So in short, as the NPRM was written you would need to register all your aircraft (for $5 apiece), they would be restricted to FRIA's (which would disappear over the next few years), and any more you build would either need to qualify as "amateur built" (we don't know what this means) or would need to be RID compliant (which is impossible due to the regulation placed on "manufacturers" which you would then need to comply with). It's a whole mess, though as of yet there isn't any actual rule in place. This was just a proposal which they'll work on before issuing a rule (probably in another several years). I would recommend you communicate with your senator/congressman regarding this issue, especially since you use foamies in education and the NPRM would completely hose that.
More good resources here: