You'll need:
2 skeins sport-weight yarn
Knitting needles 4 (3.5 mm)
Double-pointed needle, in same size
Stitch holder
Tapestry needle
Gauge
5 stitches and 11 rows equal 1 inch in garter stitch
Finished size
4 by 26 inches
Instructions
Cast on 3 stitches.
Row 1: Knit 2, slip last stitch purlwise.
Row 2: With yarn in back, knit 1, increase 1 (see how to increase), knit 1, and slip last stitch purlwise.
Row 3: With yarn in back, knit 1, increase 1, knit to last stitch, slip last stitch purlwise.
Repeat row 3 until you have 24 stitches. (Piece should now measure about 4 1/2 inches wide.)
Continue to knit across every row, still slipping last stitch of each row purlwise, until piece measures 4 inches long.
Divide (see how to divide). When you're finished, half the stitches will be on double-pointed needle and the other half will be on your working needle.
Rib across the stitches on your working needle (leave the stitches on double-pointed needle as is), still slipping the last stitch purlwise. Continue for 1 1/2 inches. Transfer these ribbed stitches onto stitch holder. Break yarn, leaving a tail long enough to weave in later.
Rejoin yarn, and rib across the stitches on double-pointed needle for 1 1/2 inches.
Transfer all stitches onto 1 needle as follows: Slip 1 stitch purlwise from double-pointed needle, then slip 1 purlwise from working needle. Repeat across row until all stitches are on 1 needle.
Knit every row, slipping last stitch purlwise, for 15 1/2 inches. (To adjust the size of the scarf, knit fewer inches for a child or more for a large adult.)
Using same method as in step 7, divide the stitches between the 2 needles.
Repeat steps 8, 9, and 10.
Knit every row, slipping last stitch purlwise, for 2 1/2 inches.
To finish: Knit 1, decrease (see how to decrease), and knit to end of row, slipping last stitch purlwise. Repeat this sequence every row until only 3 stitches remain. Bind off. Using tapestry needle, weave in ends.
