This block is a variation on the traditional Birds in the Air quilt block, translated to a 16-patch rather than 9. This tutorial makes two blocks at a time. One option for a 12" finished block is to make two sets of the 6" block and then arrange them in a four-patch.
The final look of the block will be like this if you chose to cut your 4 rectangles from background fabric:
Or like this if you chose to cut them from print fabric:
Sew and trim up the half square triangles using your preferred method. If you are going for a scrappy look, you may want to sew in pairs. If you are sticking with just 2 fabrics for the block, you can use this method to make 8 HSTs at once.
All your pieces should look like this:
Lay the pieced rectangle centered over the large rectangle (right sides together) and sew down each of the drawn lines. Cut the in half between the sewn lines.
Press the seams, and trim off the extra background fabric to get a perfect 6.5" or 12.5".