A great way to use leftover cardstock...
[click image to enlarge]
To weave a paper ATC, just cut cardstock strips down to similar widths (you can estimate rather than be ultra precise). You'll need about 15 strips of 3" length and about 10 strips 4" length. Edges will be trimmed. It helps to work on top of a blank ATC to get the spacing right. Align the 4" strips that will make the short side of your ATC. Tape the tops of these 10 or so strips to the table so that they stay put. Then weave the 15 or so 3" strips, one by one, through the long strips that are hopefully staying put. Keep the "grid" tight as that makes the finished card stronger.
Above, a few woven paper ATCs from last fall. With my stash of cardstock scraps... time to try this with the kiddos.
You'll wind up with excess of 1/2" on each side. Attach to heavy cardstock of ATC size using Mod Podge. Place a piece of wax paper or parchment paper on top and set under a few heavy books (I like to use a world atlas or a bunch of Harry Potter books) for a day or so. When dry and flat, using an exacto and a ruler or scissors, cut to 2.5" x 3.5". I did not put any edging on the card, but if you are going to send it as a gift or it will be handled frequently, you might want to add edging or some extra Mod Podge along the sides.
For more on weaving paper, with bonus photos, see Weaving Paper with Kids, where my daughter and I do another weaving project!