Assemble Pinwheel Blocks
1. Use a quilter’s pencil to mark a diagonal line on wrong side of turquoise polka dot 4" squares.
2. Layer a marked turquoise polka dot 4" square atop a red polka dot 4" square. Sew on the drawn line; trim excess, leaving 1/4" seam allowance (Diagram 1). Press seam toward red polka dot to make a triangle-square. Repeat to make 60 triangle-squares total.
3. Mark a diagonal line on wrong side of yellow polka dot 4" squares.
4. Layer a marked yellow polka dot 4" square atop a triangle-square (Diagram 2; note direction of drawn line and position of turquoise polka dot). Sew on drawn line; trim excess, leaving 1/4" seam allowance, to make a triangle unit. Press seam toward yellow polka dot. The triangle unit should be 4" square including seam allowances. Repeat to make 60 triangle units total.
5. Sew together triangle units in pairs (Diagram 3). Press seams toward red polka dot. Join pairs to make a Pinwheel block. Press seam open to reduce bulk. The Pinwheel block should be 7-1/2" square including seam allowances. Repeat to make 15 Pinwheel blocks total.