Get the UMO+ kit for sure!!! I do not think the UM2 is worth the extra money, especially since your a school and want to have the experience of building you own, the UMO is more hackable too.
I work for a school district in Michigan and have been supporting Elementary and High School 3D printing at my district since 2013 and I would without hesitation recommend the Ultimaker Original Plus Kit for your schools. We initially tried several other printers but quickly saw the major quality issues and high maintenance issues of the other brands, at the end of the 1st year we standardized on the UMO+ and have been supper happy ever since. At this point I have helped schools put together over 20 of these kits. I actually run a weekend long work shop to help schools get started. SO here’s my rational for the advice I’m offering you.
As anyone (who is not a sales person) will tell you there is no 3D printer out there that will be maintenance free and this is why I strongly advise you to consider a Kit printer. I have found crucial component to an active program is empowering building level people to run their own print jobs, do basic maintenance, and troubleshoot any issues. I have found over last few years that the absolute fastest and best way to create this building level expertise is to have a local team of 2-3 people (MS and HS kids could be part of this) assemble the printer from the ground up. This way they have first hand experience and understanding of how the printer works, how to run print jobs, and how to maintain the printer.
I have seen other kits and many require soldering, using many different tools, and many hours of build time. The UMO+ kits are beautifully engineered and the finished printers strike a wonderful balance between high quality and hackability. Team members only need to use basic tools such as a pliers and a screwdriver. There is NO soldering, NO wires to strip, NO saws or power tools. Total build time averages between 18-20 hours.
As I mentioned in my personal experience the UMO+ is by far the best for schools and clubs…as in… most accurate, fastest, easy to maintain, low downtime, large enough build area to keep up with a class of 25-30 kids, great support, very active global community, immaculately engineered, fully open source (no limits to the learning potential due to trade secrets), the box shape helps keep kid’s fingers out of the way, easily put on a cart and wheeled down the hall, winner of many 3d printer awards over the years, including MAKE: Magazine’s Most Accurate and Fastest Award, and Best Open Hardware Award. To sum up, the Ultimaker printers strike a perfect balance between reliability, durability and cost. They meet the most important selection criteria (for schools) IMHO:
1. Low downtime and everything end user serviceable. (When the printer is down no one is happy.)
2.Precision and accuracy (To insure that all kids get a good print of their model, the 1st model should be just as nice as the 500th model)
3.Speed and Build Volume (When printing for a class of over 25 kids, you need to print several objects at a time. The 8x8x8inch build volume allows for that.)
4. PLA printing (non-toxic fumes and bio-degradable) AND OPEN filament - as in you do not have to buy over priced proprietary filament from the manufacturer.
5. Open Source (No limits to student’s involvement and depth or tinkering.)
These above 5 points should help you evaluate any other printers that are out there.
ALSO - do your homework. Check out the forums where users of the printer you are considering are collaborating, and helping each other. DON’T just read the ads and look at the price.
AND AND - make sure you save $ for PLA, you’ll want a bunch of that. And make sure to get off stuff, like ColorFabb, don’t get cheap stuff since the quality of the PLA directly impacts you ability to get good prints. The High School class I helped develop (1 semester ~25 kids , uses about 4KG of plastic each time).