How would you mount an Arduino or breadboard on posterboard for a school science fair project?
Or would you suggest another way?
Which Arduino? Mine all have holes for mounting. Use nylon standoffs and nylon screws and nuts.
I guess I would use an Uno unless I found a cheaper one to risk leaving (using) in school.
I guess I would have to mount the Uno by using a board of some type on the other end of the poster board unless it is sturdy.
Thank you.
Hot glue gun? Peel it off when done.
Does it need to be functional? Or just for display?
I would like it to be functional. Something working would inspire the imagination and interest of children.
I would put inside a clear box then. Help keep any wires in place, keep it from walking off.
A clear box makes sense. My fingers were pinched by about 3 volts so I can just imagine the trouble it would cause if someone felt 3 volts from messing with it. I would probably send it in without batteries.
What you can do is mount it in a clear box like this, several sizez available at OfficeMax, Staples, online.
Maybe the fat deck of cards size box. Room for a battery holder too.
Chuckz:
A clear box makes sense. My fingers were pinched by about 3 volts so I can just imagine the trouble it would cause if someone felt 3 volts from messing with it. I would probably send it in without batteries.
I am seriously doubting that you got "pinched" by 3 volts, unless it was from some higher-than-normal amperage 3 volt source.
As a kid, I played with anything and everything electrical. I was shocked by line voltage (110-120 VAC, 60 Hz), as well as by the spark plug on a gocart engine (all times were stupid accidents). I used to build "shocking toys" from old transformers wired backwards to 6-12 volt batteries. I also played around with plenty of other battery types and sizes; 12 volt D-cell battery packs were fun to build...
Never on any of the battery packs did I ever get shocked via my bare skin.
As an adult, I've been shocked by automobile spark systems, as well as felt "tingles" from telephone ring voltages, and from a car battery (lots of current potential there!); in most cases, my hands/arms were sweaty. Even then, it was only a tingle (not a pleasant tingle, though!)...
I could imagine that 3 volts could give you a "tingle" if there was sufficient amperage available, and you were sweaty or such. But 3 or 6 volts from something like an AA or C cell battery pack?
Unlikely, IMHO...
I think the Nano is the best choice here, it has all the capability of an Uno but measure ~46mmx18mm i.e. easy enough to hide and secure. The mini is smaller still, but it is actually more expensive than the nano.
Place a small 9 volt battery terminals directly to your skin, you won't feel a thing. Take the same battery and place the terminals to your tongue, it will taste very very bitter and you will pull it away, but it won't feel like a real electrical shock at all. 3 volts is just too low a voltage to feel with normal skin resistance.
I use to go with my dad to a auto parts place as a youth in the 50s. They had on the shelf all types of carbon zinc batteries used in the old tube portable radios and other devices, 1.5, 3, 6, 9, 12, 15, 22-1/2, 45, 67-1/2, 90. I would place two fingers across the terminals to see if I could feel anything, and I found that only the 67-1/2 was worth a small threshold tingle, the 90 kind of hurt. 
Promini is least expensive, due to having no USB interface - I used a bunch of them, only connected to PC via FTDI Basic for programming.
Purchased 1 FTDI, 20 Promini, saved a bunch that way.
http://search.store.yahoo.net/yhst-27389313707334/cgi-bin/nsearch?query=promini&searchsubmit=Go&vwcatalog=yhst-27389313707334&.autodone=http%3A%2F%2Fwww.gravitech.us%2F
Promini are all installed now, keep using the FTDI Basic to download into freestanding arduino clones, like my Mini-uino's.