Here is a tutorial for the shirred girl's shirt I made last week. I used jersey knit for both.
Cut around the outside of the template, leaving generous seam allowance and wider arms. Cut the neck opening wider than a standard tshirt (the shirring later will shrink it up).
You will need two of these, exactly the same:
Unfold them and you'll have two of these. Lay the front over the back, right sides together.
Sew the seams closed from the armpit to the bottom hem and along the top from the neck to the sleeve. (Remember to leave a wide neck opening).
Below is my unfinished neck opening. Turn shirt right side out and press the seams.
First, I used my serger to do a rolled hem around the neck opening. This stretched it out even more, giving it a lettuce edge. If you don't have a serger, you could tightly zigzag it.
Wind elastic thread around your bobbin loosely. Leave regular thread in the top of your machine. Do two or three rows of stitching to shirr the neck.
Next I did a rolled hem on the bottom. This is kind of cute. I could've stopped here.
I did four rows of shirring around the bottom.
This is the view from the inside of the shirt.
Finally, I finished off the sleeves with a couple of shirred rows. On my first tshirt, I left them straight.